Two questions about combinatorics journals Hello,
I have two questions regarding combinatorics journals. I hope that this is the right place for such questions.


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*Which combinatorics/DM journals would you consider as the "top tier"?
I tried to look for an answer online, and found these two links:
http://www.scimagojr.com/journalrank.php?category=2607 and
Top specialized journals .
These somewhat contradict each other (especially regarding EJC), and I assume that the SJR ranking might not be identical to the general public opinion.

*What exactly is the difference between Journal of Combinatorial Theory series A and Journal of Combinatorial Theory series B? Wikipedia states that "Series A is concerned primarily with structures, designs, and applications of combinatorics. Series B is concerned primarily with graph and matroid theory.", but this seems a bit vague. For example, JCTA does contain many papers concerning graph theory. I also heard that the journal split due to a disagreement between its founders (or editors?). Can this disagreement shed some light on the difference?
Many thanks,
Adam 
 A: The closest thing to an official account of why JCT split into JCTA and JCTB may be found in Edwin F. Beschler's article Gian-Carlo Rota and the Founding of the Journal of Combinatorial Theory, J. Combin. Theory Ser. A 91 (2000), 2–4.

However, no single journal or set of editors, prestigious and hard-working as they might be, could overcome the tremendous diversity in hopes and aspirations for combinatorics. Competition for page allocations and scheduling soon led to intolerable strain on the editorial board and there developed a real threat to continuing cooperation and growth.

Thus it seems that the volume of submissions was a major driving factor behind the bifurcation into A and B. Theodore Motzkin agreed to be the chief editor of A, and W. T. Tutte agreed to be the chief editor of B.  The research interests of the chief editors undoubtedly played a role in the decision as to which papers went to which journal.  Some further information is provided in the editorial article Fifty years of the Journal of Combinatorial Theory, J. Combin. Theory Ser. A 144 (2016), 1–6.

The first thing that had to be done was to decide the fate of papers submitted to JCT, but which would only appear after the split into series A and B.  Together with the editors for JCTB, Bill Tutte and Dan Younger, it had to be decided which papers should be routed to JCTB and which to JCTA.  Typically papers on graph theory or matroids went to JCTB and the rest to JCTA.  This amounted to a rough split of about 40/60. Naturally, papers often did not fit obviously into one series or the other and judgements had to be made. This has remained a recurrent problem which we still face to this day.  Over the years the distinction based on graphs and matroids has become much less pronounced as, with the emergence of new subfields such as additive combinatorics, combinatorial commutative algebra and physical combinatorics, the field of combinatorics has grown significantly.

A: On your second question: I'm not sure there is an exact difference.  The algebraic combinatorics I'm interested in appears almost exclusively in A as opposed to B.  But certain areas of graph theory are, as you suggest, probably split rather evenly.  Besides just looking at past issues, look at the editorial boards.  The distribution of people relevant to your field(s) will give you a rough sense of the difference as it applies to your research.
A: The main difference between JCTA and JCTB is related to the the types of the papers that they publish. In JCTA the editors consider those papers with emphasis on combinatorics and don't accept the papers just about Graph Theory. But about JCTB the main emphasis is on Graph Theory. 
But about the best Graph Theory/Combinatorics journals there is no a unanimous agreement. One can consider journals like:
1. Journal of Combinatorial Theory Series A and B/ 2. Journal of Graph Theory/ 3. Electronic Journal of Combinatorics/ 4. Journal of Combinatorial Optimization/ 5. Graphs and Combinatorics/ 6. Combinatorica/ 7. Annals of Combinatorics/ 8. Discrete Applied Math/ 9. Discrete Math/ 10. Discussiones Mathematicae Graph Theory/ 11. Australasian Journal of Combinatorics. Although, there could be some other high quality journals. 
A: To the eye of younger folks like me who doesn't know or care exactly why JCT split into two, Series B looks like a specialized journal almost entirely in graph theory while Series A deals with a broader range of combinatorics of mostly non-graph theory kind. There are some overlapping areas such as graph decomposition. But I think they're rare exceptions. The experts in the overlapping areas may have some opinions on this. But as an outsider, I can't see any meaningful difference.
As for your first question, it's not easy to give a good answer everyone can agree for various reasons. One major reason is that it depends on how you define your "tier" and how you evaluate each journal.
For instance, even if you come up with an ideal, objective measure of the quality of a paper, it's still difficult to judge a journal. In some journals, the quality (by your ideal measure) varies greatly from article to article, so if you simply take the average, they might look mediocre even though they publish very good papers as well. Such journals typically publish more papers than picky, selective ones.
Now if you ask me how important a given journal is to my own field, I'd say a very positive thing if it attracts many good papers. But you can also evaluate journals by how difficult it is to "get in." In other words, the term "tier" can be synonymous with "league" as in "She's out of your league" if I'm allowed to employ a potentially inappropriate analogy. In this view, you might say your paper gets rejected because the referees and editor thought they were out of your work's league, and you "scored" a journal when your paper gets accepted by a glamours journal by this kind of standard. I don't think this kind of ranking is well-liked. But it's clearly of use for certain purposes, and this can be what you mean by "top tier journals."
Since you linked to the related MO thread, just look at Anna's and Douglas's answers. Anna ranks Discrete Mathematics among the top journals, and Douglas says,

In my opinion, Discrete Mathematics is only a mediocre journal (I wouldn't consider this top journal). Yes, it contains good papers, but it contains a lot of papers... on average... it's average.

If you read the blog post quid linked to in the comment, it's described as "good solid journal; not of the absolute top rank." I think you can see how people rank journals differently (probably because they have different criteria for a journal to fall in the top tier category). I'd hesitate to call Discrete Mathematics mediocre, but I think Douglas's description is otherwise spot on.
With this caveat in mind, I'll give my personal list of good combinatorial journals. Of ourse, this is going to be inevitably subjective in nature, so read it with a huge grain of salt.
But before that, there are a couple more things you should note. The first thing is that discrete mathematics and combinatorics are a huge branch of mathematics. So, mathematicians from different subfield of DM/Combinatorics may feel different degrees of prestige even if you're talking about the quality of the exact same journal by one specific standard; people can have different opinions about the same subfield. Even if a person is completely objective, the journal's level may be uneven across subfields if the journal's scope is wide. So you should take into account who is expressing their opinion.
The other important thing is that some areas don't follow the typical pure mathematical culture. I'll illustrate this by two journals that would be judged as leading, top tier venues by pretty much everyone in the respective subfields.
Proceedings of the Annual ACM-SIAM Symposium on Discrete Algorithms (Proc. SODA) is on the very top in the ranking you gave the link to. As far as I know (I'm not an expert in this field), the typical topics this publication deals with is considered theoretical computer science by many. In theoretical CS, typically conferences are more prestigious than journals, which is the direct opposite of the pure mathematics culture. This is why a "mere conference proceedings" is ranked among the top journals. And, as far as I know, SODA is a prestigious conference. (If you'er wondering if it's a math journal at all, search for my question on MO about the size of a maximum 3-term progression-free set on MO. You can find a link to an example of very good mathematical papers published in this proceedings. But you're right in that it's a computer science journal/proceedings rather than a mathematics journal. So in the remainder I don't talk about this kind of field where conferences are more highly valued.)
The other example where you should take a different culture into account is IEEE Transactions on Information Theory. It is no doubt the very best journal in coding theory, shannon theory, sequence designs, and whatnot. But it may be unfair to other specialized discrete mathematics journals if you directly compare this journal with them.
This is because, unlike the core part of pure mathematics (whatever that means), the field of electrical/electronic engineering doesn't have "generalist journals" that serve as the prestigious publication venues for every branch. This means that the leading "specialized" journals are the natural choice for highest quality papers that would go to top generalist journals if it were in mathematics.
Coding theory and other branches that IEEE Transactions on Information Theory covers do overlap with EE and CS while it is still a discrete mathematics journal (unless you don't count coding theory and such as discrete mathematics). So, if you look at its impact factor, eigenfactor, and other pseudo-objective measures, IEEE Transactions on Information Theory would look ridiculously good for a "specialized" journal. This is partly because it's actually a specialized journal that often publishes the highest quality papers.
It's true that good math journals also publish some papers that can go to one of those IEEE journals. But I don't think a lot of highest quality papers within the scope of mathematical IEEE/ACM journals are published in the best math journals. Because of its clear leaning toward the kind of mathematics that is typically not the central topics of prestigious math journals, this effect seems much more pronounced than on JCTA and the like that also cover coding theory etc.
Also, the best journals in physics such as Physical Review Letters publish highest quality papers in quantum information theory. IEEE Transactions on Information Theory also covers this field. But it isn't a physics journal per se. If your paper is more about information theory than physics, it wouldn't be strange to publish it in this "specialized" journal if you think your work is of the highest quality. So, this is another reason you can't clearly say it's a specialized journal which is less prestigious than the best generalist journals (although the editors of IEEE Trans. IT expressed concerns about the fact that the journal is losing ground in quantum information). So, you can't really say it's a leading specialized journal in DM/combinatorics although it clearly is in terms of quality, prestige, etc.
So, with this verbose caveat in mind, I think JCTA/JCTB/Combinatorica/IEEE Trans. IT would be on pretty much everyone's top tier journal list. And if one of them doesn't make it, I feel like it's probably because of the person's preference in branches of discrete mathematics.
There are other journals I think can be on someone's top tier list too. Journal of Algebraic Combinatorics and SIAM Journal on Discrete Mathematics come to mind, for example. Also, I wouldn't be surprised if you submit an excellent paper to Electronic Journal of Combinatorics. I'm not an expert, but as an outsider, Random Structures and Algorithms looks pretty good.
I like Discrete Mathematics for the reason I already said, but I know it may not be a top journal depending on exactly what you're asking. Also, journals that cover some niche topics may receive more positive reviews from some (e.g., Journal of Combinatorial Designs and Designs, Codes, and Cryptography), although it can't be "top journals by the vast majority's standards" for obvious reasons.
As I said, combinatorics is wide. So, there are many journals and many subfields I'm not familiar with. So there must be many good journals I failed to mention. And those I mentioned may not be as prestigious to other people. The only way to know the accurate ranking by your standards is to read each journal for yourself.
Oh, I almost forgot. If by EJC you mean European Journal of Combinatorics, then I'd say it's a bit overrated in the ranking you gave. But it's a good, solid journal by any standards in my arrogant opinion, and I wouldn't strongly disagree if others say it's underrated.
Last but not least, take this つ[salt]. You don't believe what a random talking duckling on the internet is babbling about.
