-Controllers have built in battery, so they are usually charged and I can play via wirelessly (my 360 play and charge kit battery doesn't last long and I usually have to play games wired).
-MS consoles have issues working for me. WTF?
-I have two PS3 consoles to play on.
-My slim PS3 uses less power than my 360 (which is an older one). ????
-I prefer the Dual Shock 3 controller for games.
-My PS3 is much quieter when playing games (disc drive doesn't make loud noises).
-My 360 HDD is only 20GB, compared to my PS3 HDDs being much larger. hahaha
-More friends on PS3 usually. Friends? lol.
-Slightly care more about my trophies than achievements.
-Prefer the look of PS3 game cases. Cases are important for game quality.
Some games I'll buy on both platforms, like Modern Warfare 2, or if there's an advantage in 360 friends owning it. I even bought Bayonetta on PS3.
Those are some damn good reasons.