Honestly, Halo3 was the single reason I wanted a 360... but in retrospect, having now had a good go at both systems I have to say I made the right choice.
The PS3 is technologically more sound, more powerful, has blu-ray.
The 360 meshes into my home network as close to automatically as you can get, plays my media library straight off any windows PC in my house, the DVD drive loads games much quicker, the interface is intuitive enough for my wife to use it to play her downloaded tv shows without my help (I have to help her light the oven). And to be quite frank I've been weeabooed to death. I'm loving the scarcity of "big-swords, pointy hair and subtitles ofver unintelligible shouts in Japanese" titles... yes I know DOA is XBawks but I sold my copy because it got booring and repeditive after about say... oh 1990. (sorry Imax... but Killzone was fun for about 10 minutes, and then I spent the next 2 years hating it).
The 360 gets more useage time than anything else as a media player. If I'm lucky I get to play games on it.
Did I mention just how EASY online gaming is on the 360?
If the games you want to play are only on the PS3 then get that, but if you don't really care and want added ease of home integration then get the 360.
P.S. I also do not own a single Blu-ray disk and haven't bought a DVD in about 2 years.