Interesting. It's gonna be a tough choice between the two consoles but I will probably go PS3 because I will stop paying for 360 online when the PS4 comes out.Rockstar is developing it separately for each platform so each version should take advantages of their respective systems. If there are any differences with multi-platform games these days, it seems to be between slowdown (usually a 360 problem) vs v-sync errors/tearing (usually a PS3 problem).
I still have a hard time believing this game will run smoothly on consoles but most previews have already said Rockstar demo'd it using the PS3 or 360 and I haven't seen any disparities.