Only buy a 360 if there are XBOX exclusives that you are really interested in. Otherwise, most games are multi-platform, with minimal (if any) difference between them. The release of the 360 was really farked up, with RROD, no HDD, no built-in WiFi, only a 20 GB (13 formatted) hard drive in the Premium, etc. It's kind of silly that a consumer has to "Jasper hunt" to try and find a console that won't die on them.
I find Live to be a better experience than PSN, but then again, you pay for it, so it better well be!
One thing about Live though: voice chat is built in, and all 360s come with a mic, so expect lots of little "kidz" cussing at you...