After playing most of the AAA titles on both systems... go with a PS3. I never have to worry about my PS3 getting a RROD, paying for online gaming (which the Wii gets for free also), or hoping that I have enough room to install a game to keep it from getting choppy. I haven't touched my 360 for about 2 months now since I got my PS3. If I didn't have Rock Band 2 with the instruments, I would've sold mine already. :/ I will try to layout the facts, but when it comes down to features and stuff, look at what kind of games you want to be playing. Even though they share 90% the same library, I can't shake the fact that PS3 is, and will be the way to go.
360 Pros:
Lost Odyssey and Marvel Ultimate Alliance (with the DLC :p) rocks ^__^
Has some great XBL games (Castle Crashers, Shadow Complex)
Has a very good controller (comfortable layout)
Decent media options (Netflix, IGN tip videos)
Avatars and Achievements

360 Cons:
Overheating, I always have to have a fan by mine. On my second 360 now, both of which RROD'd not even a week after I got them
Small HDD, cost over 100 bucks for a bigger one (not sure how much the elite has though), could only install 1 game at a time :/
Have to install games just to keep the DVD drive from making a grinding noise and ruining the disc (3 new games already have small circular scratches T_T)
D-pad on the controller
sucks. One minute you're pulling off hadoukens, the next your guy is leaping... made me take back Street Fighter 4. :/
BIAS:Exclusives games just aren't that great (Gears 2 is fun, but the excitement wears off after you beat the game, and Halo 3 felt too generic)
Confusing point system for buying games
PS3 Pros:
Tray-less DVD drive, which you will come to love

Free online gaming (which gives me money for PC MMOs :p)
Massive HDD and other features (Blu-Ray is a great improvement... if you have a 1080p screen to tell the difference :/)
Can plug in a USB keyboard mouse to play Unreal Tournament 3, or makes webbrowsing and messaging friends way easier.
FACT:Metal Gear Solid 4 is one of the best games I have ever played... even if the story is lost on me. Everything is topnotch and well produced.
BIAS:Better exclusives (Uncharted plays like a movie, MGS4 IS a movie with controls, LBP is a blast, Killzone 2 is the best looking FPS I've ever seen [1080p monitor], Valkyria Chronicles has some deep characters and an even deeper combat system, and inFAMOUS is one of the best open-world/comic book games ever made). These all feel mature and are rather solid. Maybe the Resistance and Ratchet & Clank series aren't that enjoyable to me, but the ones mentioned are all strong games. PS3 is even getting 360-exclusive games with more content, like Tales of Vesperia, or Eternal Sonata.

PS3 Cons:
The L2/R2 buttons cause your fingers to slide off (fixed by grabbing
these from Gamestop)
PSN store is kinda layed out weird
Trophies are very "meh" to me.
Got mine for 400.

Doesn't come in Shiney Dark Green or Blue.
See what games you want, check the video reviews, and make your decision. :p