The only problem with Mr. McMahon (and there was a problem) was that as a spokesman / authority figure, you were always going to be deprived of the big, classic showdown between him and Steve Austin (or Rock, or whoever else he was feuding with at the time). Yes, there was the cage match at St. Valentine's Day Massacre, but do people remember that match in the same vein as an Austin/Rock, Rock/Hogan, Hogan/Warrior, Warrior/Savage or Savage/Steamboat? No, and that's kinda the point: by putting half the focus on someone who can't live up to the billing of 'wrestler', I think it started the gradual descent into what wrestling is today—entertainment with wrestling as an ancillary component sometimes. Would I trade the Attitude Era now? No, considering how huge wrestling was for me back in the day. But it's worth noting, I think.
If we're looking at greatest heels, we must consider two categories: those who were either lifers (or spend significant chunks of their careers as heels) and those who had spectacular heel turns that basically solidified them in the club. In the former, you've got three guys ready-made in Randy Savage, Ric Flair and Roddy Piper. Those three guys in the 1980s were larger than life without being the jacked up superhuman that Hulk Hogan was. Into the 1990s, Vader was a pretty great heel with some great matches. In the other category, there are two that immediately come to mind: Hulk Hogan's turn by joining the nWo, and Bret Hart's turn by regrouping the Hart Foundation.