PS3 will be better for RPGs but Xbox360 will be better for FPS (Xbox always has)
So, wait, both of them will excel in a an often crap genre which is in the majority of cases (but not all for either of them) repetitive and tedious? Okay, fair enough. I respect your decisions.
Personally, I pick the system which excels in Platformers (Mario), Adventure games (Zelda), simulation games (Animal Crossing, and sans BtN, the best Harvest Moon games tend to be on Nintendo systems), Strategy games (Fire Emblem! Maybe Pikmin and ____ Wars, too), Fighting games (SSB... online... *drool*), racing games (between F-Zero and Mario Kart, you've got all the
good subgenres of racing), and also GOOD RPGs (Paper Mario, hopefully another Tales, hopefully a Mana game, any other RPG with GAMEPLAY) and GOOD FPS' (Metroid Prime, the break from the constant mindless repetitive FPS tedium). Yeah, I actually look forward to systems for a variety of reasons, rather than touting a single example.