I'm guessing that the longer the needle the better. It seems like you'll get significant experimental issues from the cases where the needle just barely crosses-or-doesn't-cross a line, and if your needle is long enough to cross lots of lines then this becomes less relevant. Probably you want to color the lines so every tenth and every hundredth are a different color, the better to accurately count them.

I'm guessing that the longer the needle the better (meaning, highest $\ell/d$ ratio). It seems like you'll get significant experimental issues from the cases where the needle just barely crosses-or-doesn't-cross a line, and if your needle is long enough to cross lots of lines then this becomes less relevant. Probably you want to color the lines so every tenth and every hundredth are a different color, the better to accurately count them.