In San Francisco, 49x19 worked well, though I think many MANY people ran 49x18. That seemed to be the standard ratio.

After I moved to LA, and I switched to 49x17 and it seems to do pretty well for lack of hills. Of course they are harder to skid but I think I can get used to it, and I get to go faster more comfortably, which is important cuz LA is so sprawled out.