Speaking as someone who's played both, I prefer PS3. It's why I bought one. Contrary to popular belief, (looking at you, SantaUno) the XMB (say it right, it ain't a dashboard) is FAR more simplistic than people are making it out to be. Everything has it's own category, and while some of the more advanced functions (apparently Santa never thought to press the TRIANGLE button) escape some, it's fairly easy to figure out. Playing is easy and fun, and the only issue I have is with no changing in-game music and party chatting while playing different games. But guess what? Microsoft patented both of those, so it ain't happening.
Speaking of patents, since Nintendo takes out a patent on everything they make, I am surprised the PS3's Wand and the 360's Natal have made it this far...