Starting tonight, Demi Lovato and Britney Spears will judge contestants on The X Factor Season 2.

But before we watch these young superstars hand out compliments and critiques, let's do a bit of both ourselves, shall we?

The singers walked the red carpet of an X Factor premiere party in Hollywood last night, with Demi donning a short black skirt and Britney feeling a lot more blue. Which pop star pulled off her outfit best? That's for us to ask - and you to decide!

Compare. Contrast. Vote now.