It depends on what you want to do with the system. If you want a gaming console then the 360 is by far and away the better choice. The choice of games is better, the online side of things is way better and it's generally a better machine for that.
I know you have to pay �40 a year for Live, but it's worth it. Having to pay means the little turds that often ruin PC gaming are excluded as they don't have a credit card, Microsoft are more on top of removing inappropriate content and the performance of the dedicated servers are better. You also get a headset as standard and all multiplayer games have voice chat which is far more sociable. You can also download movies and music through Xbox Live
If you want an entertainment system with a Blu-Ray player, then buy the PS3. The online side is free, but I haven't had a decent online game yet with people glitching and connection issues.
I own both, but the PS3 hardly ever gets used for gaming - I play LIttle Big Planet and that's it., but I watch a lot of Blu-Ray films. The 360 gets used almost every day.
The 360 is also cheaper, with Blockbuster doing the 60Gb version plus three games for �199 whereas the 80GB PS3 is �100 more with no games.