Let's see here...
In one corner, we have CM Punk, who is prominently featured in main event storylines on the flagship show, the man who will have main evented two straight pay-per-views come Sunday, the man who has actually been number one in Merchandise sales at some points over the last year, the man who got more than 18 seconds on the grandest stage of them all, the man who is currently featured in the biggest current storyline in the WWE. The man who is featured on the cover of WWE 13, the man who is actually placed in dream match scenarios (Yes, he has reached dream match scenarios as the second biggest name of the current generation, the Savage to Cena's Hogan) with Stone Cold Steve Austin on a regular basis, the man who will more than likely main event every PPV from now until the Royal Rumble atleast.
Then we have Sheamus, who hasn't main evented a single PPV since he became World Champion, has constantly been featured on the B show and not the A show, with no dream match scenarios imposed upon him (because he isn't on that level yet, hopefully someday he reaches this), has never ever came close to topping merchandise sales EVER, probably won't main event a single PPV during his tenure as "World Champion" (although someday he'll probably be THE GUY on Raw for a year or two), not to mention he wrestled the fucking OPENER at Wrestlemania.
Gonna have to go with Sheamus on this one