Probably Tobi for me.... I think they should have kept Pain's true appearance hidden until he showed up to kill those fodder at the gate... Keeping his appearance to be a mystery until it was time to act.
Tobi had his personality hidden, and when it was revealed it showed, cunning, ambition, history, and mystery. Sadly Pain was shown before his fight, and was suddenly demoted from leader to Number One Servant/Apprentice... Which sucked because Pain definitely would have been better had he not been revealed and shown not to be in charge until after his defeat.