Character wise, Daniel Bryan should be up there, but he's just so naturally over with the fans it's not quite like that. If he was a character in a book, we'd all fucking hate him, it's just his insane charisma and how he connects with the crowd that not matter what he does, he will never get booed properly.
Bully Ray, Bobby Roode and Kevin Steen are great heels. In WWE, we have Laurinaitis and Vickie, which says what's wrong with WWE atm. The most over heels aren't wrestlers. Daniel Bryan plays his character well but I wouldn't call him that great tbh, at least not compared to the rest of them. Just a shame Bryan is the only heel wrestler in WWE that gets mic time along with the newly turned heel Big Show. Guys like Ziggler and Rhodes in particular get nothing even though both of them probably can play a heel character as well as a Daniel Bryan imho.
Bobby Roode & Bully Ray by far are the best heels right now. Roode & Ray both play good assholes. Bobby is also the most dominant TNA Champ ever, and one of the most dominate champions in pro wrestling right now.
I haven't watched a lot of TNA, but have seen a little of Bully Ray and Bobby Roode. They're pretty legit. I feel like Brock Lesnar had instant credibility as a heel when he returned, but he's not on TV enough, then he also beat Cena like a child and still lost. Bryan is the best heel in WWE, and I think Ziggler could be, if given more mic time and pushed a bit more.