7. Groot - Andy Serkis
Groot is one of the best characters in Guardians of the Galaxy, but he's also probably the most challenging to bring to the screen well, given that he's an eccentric tree creature who can absord wood in order to rebuild himself in the event of "injury". He's also able to increase his size, is impervious to fire, and can control any trees in the vicinity, and though he's primarily a gimmick character, he's also one of the universe's most intelligent characters. Thus, we need an actor who is both adept at playing otherworldly characters, and who can convincingly play a super-smart person. Assuming that Groot is going to largely be composed of CGI, is there anyone else better-suited for the role than Andy Serkis? Through his performances as Gollum, King Kong and Caesar, Serkis has proven himself the master of performance-capture technology, supplanting his indelible personality onto these unforgettable characters and in that stead changing the way we view acting. As such, he's the only logical choice for Groot, as he'll be sure to breathe a very human presence into what could easily be a vapid, empty CGI creation.