If I can say a few things in favor of the Xbox 360 (not being a fanboy, but they are often overlooked)
1: Games on the 360 are typically more stable/better looking than they are on the PS3. It's not as jarring as say, SNES VS Genesis, but the stability thing can lead to problems. Developers are STILL having problems properly developing for the PS3. The perfect case of this is with Skyrim, where it looks like the system is not capable of running their DLC packages. Also, the PS3 firmware gets updated more than Microsoft Windows. You can expect a firmware upgrade nearly every month. Normally this doesn't sound like a big deal, but when you consider that A: It's a completely new firmware so the file size is greater than 100MB and B: Sony's network is so atrociously slow it's like your connection speed has slowed down to entry level DSL, it can get quite annoying. Games are often patched as well, and some games need to be installed. It's not uncommon that you can pop a game in and try to play it but the game needs to first download updates, install trophies, then install to the HDD. It's like playing a game on a computer, and sadly it's not that surprising for you to put a game in at 8:00 and not be able to actually PLAY it until 8:30. Finally, the PSN goes down a LOT for "maintenance," and oftentimes they'll just do it in the middle of the day US time, as opposed to say like 3am EST. The 360 gets about 2-3 major updates a year, and the network almost never goes down, and even if it's for maintenance it's often done when you're asleep. So if you want the least amount of issues, I'd say go with the 360.
2: Microsoft usually cuts deals with publishers for first access to DLC content, which means if you have the 360, you'll get access to certain DLC weeks to months before PS3 and PC gamers do. We've seen this with the Call of Duty games, as well as Skyrim. It should be noted that Sony has had some exclusive deals as well, such as with the Assassin's Creed games, but typically, major AAA publishers go with Microsoft as they have deeper pockets than Sony. So with the 360, you'll often get new stuff quicker.
3. Microsoft requires all their arcade/downloadable games have free demos. This may not sound like a big deal, but it allows for MUCH more access to potential content, and is a good "try before you buy" system. You're LUCKY if you can find a PSN game that has a demo, and what really stinks is that most if not all of their exclusive games don't have a demo, and usually cost upwards of $15.
Just some stuff to consider.