I'm asking this question from the perspective of someone who just wants to read journals rather than contribute to them. For the purpose of this question I'm using the definition of Open Access in the sense of the Budapest Open Assess Initiative:

"By 'open access' to this literature, we mean its free availability on the public internet, permitting any users to read, download, copy, distribute, print, search, or link to the full texts of these articles, crawl them for indexing, pass them as data to software, or use them for any other lawful purpose, without financial, legal, or technical barriers other than those inseparable from gaining access to the internet itself. The only constraint on reproduction and distribution, and the only role for copyright in this domain, should be to give authors control over the integrity of their work and the right to be properly acknowledged and cited." (From the BOAI FAQ)

I'm aware of the mathematics journals listed in the Directory of Open Access Journals but I have no way of finding out from that list which journals are most respected by the community.