I had my reasons. One of which being Forza. And the other was my friends. Also in the beginning, Xbox was being pushed as the central entertainment system for your living room, and PS was pushing games. But as it got closer to release, there was a flip flop. Suddenly Xbox was all about the games and pulled a bunch of things people weren't interested in. At that time, Sony decided to push the home entertainment center non-sense.
All of that together is why I chose Xbox. And yes, I have been recently regretting that decision.