360 and PS3 are different. You are no doubt going to start a flame war if you say that they are better than the other. Before I go on into my long paragraphs, buy the one that your friends are on. The really popular games are for both consoles... with a few popular games of similar calibur going to different consoles (Halo is popular on 360 and Killzone is popular on PS3). If you plan to play online at all, play with your friends. The popular multiconsole games are similar enough to not have you notice. If all of your friends have 360 and you have a hard time drawing a preference, play 360 to get on with your friends.
Like I said, the consoles are very different but very similar. They both have VERY good games. The controllers both work very well. Xbox360 has its XBL system. XBL is a $60/year service, but you get a bit out of it. Sure you have to pay for the ability to play online, but you get a few features out of it. The biggest features deal with actual gameplay. 360 online games are a TINY bit less laggy than PS3, and I have found that the players online are a bit better... probably due to winny kids not wanting to pay $60/year (although there will always be winny kids playing video games too mature for them). 360 has Xbox Arcade which I have to say is much better than the similar PSN service. There are just way more amazing arcade games... if you care for it. 360 has double the RAM of a PS3... so that is fun. Contrary to popular belief, it has less (barely) graphics capabilities than the PS3 (500MHz vs 550MHz... woo). 360 has access to Netflix and can function as a very nice home media center.
The PS3 is also very powerful. It is the least expensive BluRay player on the market... so that right there is an immediate plus. You will not have BluRay movies if you do not already have a player... but just consider it ;D PS3 has slightly better hardware (save for RAM), and the interface is a little bit smoother. While it does have free online, the players online seem a little bit more... eh... IMO. PS3 can play PSI and PSII games if you want, and it can hook up to your PSP if you have one. Having big hands, I prefer the 360 controller to the PS3 controller... but it is still very well built. The PS3 has a few more good exclusive games, but if you are like most players, you will probably end up playing CoD, a single exclusive game from either console, and a few other games that the consoles share.
Once again, don't listen to the haters. Both machines are very powerful and are very worth your money. Ask around with your friends who you would want to play with. See which console they play. If you have no friends, or there is a 50/50 split between them, I would lean towards 360 BARELY just because of the Arcade games. I am a sucker for good games like that... and I have wasted 100s of hours of my life playing $10 games on the Xbox. ;D