I think racing games and fighting games are best played on the PS3, the 360 has sports and shooters and the wii has platforming and adventure games. RPG's are tough to call because I don't know that there has been a must play RPG for sometime now and FF13 is on both HD consoles. I have high hopes for last story and xenoblade though.
I have always been a Nintendo gamer because I'm a fan of action/adventure games and platformers, and mario zelda and metroid are the meat and potatoes of that genre. I don't like sports or racing games, but I don't mind the occasional shooter, so I think the 360 is a better fit for me. I really wanted to play Uncharted because it's right up my ally, and now I have, so what else does the ps3 have to offer me?