I'm waiting till both are out before making a decision, but I'm leaning towards PS3 because of the faster loading times. But...
Whatever console I am buying it for, I'll also buy some arcade sticks, and so that pushes me towards the 360 version since I have UMK3 and SF2 (with hi res version coming out soon) on it.
But then again, SNK is going to put their library on the PSN.
So it's a hard decision.