Straight Machamp would be sufficient, but I would most likely recommend a SP Deck.
I know a kid, who came 6th at worlds, that is going to be there, and other people I know have SP decks and Donphan decks, and some with Machamp.
I would recommend run a SP deck with Mewtwo level X line of 1-1, also include atleast a Machamp counter, I would suggest Toxitank. Toxicroak active, with expert belt and 2 energys, while a stadium in play and skuntank G in bench to poison the opponent by it's ability. Which means Toxicroak G will hit 80, and it's ability prevents Machamp from knocking you out/ Donking.