I'd go for for 360.
The big advantages to owning a 360 are access to the 300 titles already in it's library. A load of AAA titles. In the first 7 months of the PS3's release it only had 16 games with an average rating of 70% or above, whereas the 360 had 28 games with 70% or above (And a higher average score) in it's first 7 months. So during both consoles respective timeframes, the 360 has had more success with the amount, and quality of it's games.
Thus the 360 has a strong past, and a very strong future. This fall the big PS3 releases are Lair and Heavenly Sword. The latter looks cool, but Lair recently got 5.5/10 in EGM. The 360 has Halo 3, Mass Effect (From the best western RPG developer. The game is beautiful and huge), Bioshock (Currently reviews are all 10/10 aside from PC gamer which gave it 95%, their second highest rating ever after Half-Life 2), Lost Odyssey (JRPG from the father of Final Fantasy), GTAIV (With exclusive 360 content), Half-Life Orange (Half-Life 2, episode 1, episode 2, Portal and Team Fortress 2 all for the price of 1 game) and more. Both consoles have these: Call of Duty 4 (Exclusive open 360 beta coming next month), Rock Band, GH3. Overall, 360 has a good few more exclusives and the gaming line-up for it in 2007 alone is astounding.
Xbox Live is currently the largest online console community. It is smooth, lag free (For me and my friends at least) easy to navigate and straight to the point. Home looks ok, but I wouldn't go on it much. I'd rather turn my console on and instantly join a match from the menu in front of me rather than having to go onto an interactive world, fiddling about with 'apartment' to meet friends and going into the 'trophy room' to see achievements. I am aware that you don't need to access Home to join a game, but to me that just leaves home as an online MySpace type world. Second Life for the PS3. It wouldn't add to my online gaming at all. And you have to pay to even decorate your apartment. 360 DLC is usually fairly priced, aside from GH2 content. $5-10 for a great arcade game or game add-on is fine. A lot of it is free too, such as the great Key to the City DLC for Crackdown. I'll stick with buying actual games, rather than a new couch for my online house.
PS3 advantages include Blu-Ray if you're interested in HD movies (Though the 360 has an HD-DVD add-on and the ability to download HD movies off their Video Marketplace) and their respective exclusives. Screw online, and power, and blu-ray though, these are GAME consoles and it should always come down to which has the best games to play for you. It is purely down to opinion. They've both got great multi-platform titles, but it comes down to the exclusives. So far, the 360 has more I think, and it's slowly garnering once PS3 exclusives (Devil May Cry, Ace Combat, GTA etc) but if you're a huge MGS and Final Fantasy fan, for example, and you have no interest in 360 games, obviously stick with the PS3. I don't think you'd be unhappy with either console, but at present I think the 360 offers a lot more.
This is an excellent thread, with well thought-out arguements on both sides and without all the fanboy posturing.
Based on what's been said here, I'm leaning towards PS3.
I have a PS3 but plan on purchasing a 360 once they drop the price in August.
The fact that most of my friends have gotten a 360 makes me feel like i should since most of them are moving away here at hte end of summer to go to different colleges. Also the price drop coming up is pushing me to get a 360.
And the price drop (according to all the circulars) doesn't look like that much...
The price drop is $50 per SKU. In the UK they're giving away 2 free games too with the premium.