Too true, but I would say Williams.
Also, I think the biggest FM wannabe I've ever heard is that guy who plays Fiyero on the original Wicked soundtrack. Oh God. He's an excellent singer, but their inflections are practically identical. Not to mention that onstage he looks flaming.
I am the greatest F.M wannabe! I even go around the Munich nightlife rupturing the anuses of young rentboys, just so I could copy him.
And I bet Robbie and Justin haven't quite gone THAT far with their idolizing...