It's Demi Lovato — By a Nose!
While both Lea and Demi are just about 5'3", Demi is just slightly taller — she has three and a half inches to Lea's two and a half.
We think Lea would be a great replacement for Demi — which obviously has nothing to do with their very and although Simon wants Miley Cyrus in Demi's spot, we think she'd be a better replacement for Simon himself. (Sorry, bro!)Did you guess which singer is taller? Click here to play more Guess Who!