XBMC, which one?!

I ordered my RPi yesterday, so it should be arriving some time next week.

I've decided to use it as a media player with XBMC installed (duh!)

Now I'm wondering whitch way to go? I'm using a Class 10 SD-card.

Raspbmc? Xbian? OpenELEC? Or running XBMC on Raspbian?

Which is the best? Which is the fastest? And so on.