I really thought Sheamus given the opportunity would draw more heat than CM Punk, but what helps Punk is that he works well with an entourage....
Sheamus would be a bigger heel but WWE Senoir Executive Kevin Dunn has an issue with Sheamus which is why Sheamus is being buried so much which is a shame. Sheamus is without question one of the better young talents. The weird thing is even though Sheamus is in good terms with Triple H, it seems Kevin Dunn has more say.
id say punk is the top heel del rio is 2nd and then the miz i'll admit punk gets cheered more often then the other two but jericho was the top heel for the past couple of years but he got chants because of the respect for his abilities.
As for sheamus generating heat he seems to get booed more when acts like a bully usually with someone smaller so with this feud with mark henry nobody cares for it because if it was real or shoot mark henry could snap sheamus like a twig.
Back on topic if given time i think del rio could be a top heel,tweener or even a face(i think it could work just he does work better as heel)