Its too soon to call. Look at the main event heels now. you have sheamus, the miz, and barrett on raw, del rio and kane on smackdown. who were they a year and a half ago. sheamus, barrett, and del rio werent even on tv, kane was jobbing to main eventers as a face, and the miz was a blimb on the radar screen. they make new m.e. all the time, so it very well could be someone we havent seen yet. but to be fair, ill answer your question with a current wrestler.
i'd say barrett
sheamus is too white, hhh is on his last leg, they wont make del rio the face, rey rey is also on his way out, taker wont be around too much longer, the miz is too small, edge will only be around for about another 3 years, jericho does best as a heel, etc.
barrett has it all. the looks, the size, the charisma, the mic and mat skills. i didnt care for him too much when he first debuted, other than being jericho's (my favorite current wrestler) rookie. yet he is doing very well in the main event scene, and can put on compelling stories. even with super cena. if its no one else, in 5 years, i can see barrett as the man.