I'd prefer for him to be a heel. He just has a personality of the more heel variety. He would have been an awesome heel back in the days of Harley Race, Ric Flair, Roddy Piper, Freddie Blassie, Ted Dibiase, etc. An era where people could become so hated, even to the point of receiving death threats and having fans jump the railing to go after said heel, just because people thought wrestling was real. Nowadays, Punk just gets cheered because he's too 'cool.' They know he's just playing a character when he insults the crowd. I can tell he could have got people so worked up back in those old days if he was around back then. Part of me thinks he was born in the wrong era.
Anyhow, I'll be willing to forsake a Punk/Brock feud just so Punk could stay heel and team up with Brock, as the two would make an awesome duo. But a split centering around which one Heyman prefers (however that comes about) is almost inevitable.