In terms of who gets the best heel-reaction from a live crowd, it goes to John Cena each and every time. Even in a pro-Cena town, he usually gets more boo's than 90% of the heel roster. It's not a good or bad thing, necessarily, it just speaks to his incredibly popularity...
But as for who is the best ACTUAL heel -- meaning a guy that is supposed to go out there and get the crowd to hate him (altough I'm still not convinced that isn't their focus with Cena as well) -- I'd have to give this one to Mark Henry. That is, when he's not injured. If we're only counting active wrestlers, he's probably out, but Henry is the only guy to really go out there and get a pure heel reaction every time he hits the ring. He's big, mean, evil and he likes to inflict pain. Henry and Kane are the closest things you actually have to heels in the WWE right now, because they aren't getting face reactions like Daniel Bryan or Dolph Ziggler does on a weekly basis. Don't get me wrong, I love them, but they're not doing their job as a heel, which is usually to help get a major face over. The only reason I'm not considering Jericho is that he's lost every major match since returning, and it appears as if they crowd just don't give a single fuck anymore.
Now if you throw in managers and on-air personalities, John Laurinaitis wins this competition hands down. A picture of the guy is shown, and the entire crowd erupts into boo's. He's come a long way, developed an actually character -- the character intentionally sucks, but I swear to god it's there -- and is a genuine heel personality in the WWE. I actually like what they've been doing with him and Eve.