In terms of online the Xbox 360 has a distinct advantage. One of the best parts of the current generation are the Arcade titles and aside from the retro titles Xbox Live is the best and every single game comes with a demo. It also has a distinct disadvantage. As the console will likely be your third system, unless you have more friends with Xbox + Live it may not be worth it for you to pay for online on what is a less important system. Also don't forget the classic Xbox 1 titles are also available for download which you can't get anywhere else.
.In terms of game library I would say the Xbox 360 and PS3 are about equal, however the Xbox 360 does win out with the older titles both playing better on the Xbox 360 system, not coming with mandatory installs and because the system was out longer a wider variety of cheap and really good budget titles. Also remember the Xbox 360 is backwards compatible to last generation unlike the PS3.
I say it really doesn't matter which system you get. I prefer the Xbox 360s online and to me if I played online games I would go straight to the Xbox 360 system but I hate online gaming so its a moot point for me. The best part is the fact that games against people over seas has far less latency and coming from Australia/New Zealand thats kinda important as a lot of the possible opponents are going to be overseas.
Tease.
