The Xbox is more group friendly and tend to more more multiplayer capability. Gears of War 2, and Halo 3 are some of the games that tend to follow this. Also the 360 has a a lot more DLC. I know the PS3 has some but not as much as I would like. The final think about the 360 that I have to say is that I personally find the 360 a little easy to find points in most games to give yourself a break, and don't make a joke from that last line.
The PS3 has the best graphics, it had to be said. I know the 360 has a couple games that have very good graphics, but compared to the PS3 they're not even close. The PS3's games are mostly single player which I love, this also gives the games a lot more original content. Also most of the new revolutionizing games are on the PS3 such as Killzone 2. Now that the are more games on the PS3 it has more ground to stand on against the 360.
Now let the first Gamer's arena start