If you are still looking at this, I can lend a little light.
Get the 360. I have both, and really don't use the PS3 anymore. Gran Turismo 4 was so boring and un fun compared to ... well ... any other racing game on the market. I went back to 3 and even 2 and had loads more fun.
GT5 looks good, don't get me wrong, and prologue was neat, but Forza 3 is just a more polished game, that makes an effort with it's players to bring them what they want, VS GT ... GT doesn't see that they have competition so they just make the same game.
Although ... with the release of Prologue, maybe they are trying to do something more. We shall see.
BUT, you also like shooters. I just like how the whole online system works, the online ranking the voice chat/team chat systems ... the party system is fun and easy also. I like that my headset plugs into my controller and not a bluetooth thing I have to worry about syncing. I like Xbox hardware.
Ps3 - the new slim is very neat looking, and i like the way it was put together (i've seen the take apart photos on Kotaku). I DON'T like that you can't put linux on the new slim, but whatever, that's a small thing. The blu ray is awesome, the PS3 network games are REALLY damned cool. BUT ... microsoft has been making huge strides recently on their Live games ... so they are about equal.
OH ... yeah ... the ps3 does these annoying update things, whenever they release an update it takes about 40 minutes and then it has to install. Sheesh, for the love of god man just LET ME PLAY! Same thing when you download an add on ... new tracks new whatever ... you download then have to install then have to update. Ugh.
BUT ... the PS3 does have Little Big Planet.
I'unno. Man, the new Xbox is really sweet, quiet and runs like a hardcore champion. It takes a lot more to break one of the newest gen systems than the older ones. (I have been repairing these damn things for 2 years now.) I can also tell you there is no permanent fix for the RROD, just replacement.
Microsoft is pretty good about the RROD fixes, they are MUCH fewer now and get them done in a couple weeks. Usually they just replace them. Stores are pretty good about it too, usually just swapping out the unit.
I have both, I like both, but I use my 360 more. Out of all my hardcore gamer friends, it's all 360 ... then a ps3.