I listen to a handful of podcasts focused on the history of pro wrestling, and I enjoy watching old tapes. Usually those tapes focus on Mid-Atlantic and Southeastern/Continental Championship wrestling before I was old enough to watch because those were the two promotions which regularly promoted in northeast Tennessee and Southwest Virginia. While outside of Ron Fuller's Studcast and the occasional guest appearance by Beau James on Between the Sheets there is rarely content around the Mountain Empire happenings of pro wrestling, I absorb what I can, and then check out other cool stuff like Mid South (Louisiana-Arkansas), Memphis, and old Nick Bockwinkel stuff in the AWA.
One of the podcasts I listen to is hosted by John McAdam. While he focuses on the northeast, he posed an interesting question- who are the best heels of all time? He used the "Mount Rushmore" model to limit it to four.
I don't know if I can do that. From those older tapes, there are two completely distinct types of heels- the ones who can get their own heat both through their ventures in the ring and talking, and the monsters who used mouthpieces (like Abdullah the Butcher) to get heat. Here are my lists, highlighting the two very distinct groups. With so many folks who came around post Hulk Hogan/WWF expansion, you should check out their work where you can find it. (If you ask me to post clips, I am happy to do it.)
The Talking Heels:
The Masked Superstar (later became Demolition Ax)
Don Carson "The Big C"
Pre-Horseman Tully Blanchard (see 1984)
Mid-South Ted Dibiase
Nick Bockwinkel (still the best heel champion of all time-yes better than Flair)
1970s heel Jerry Lawler
Jos LeDuc (also an excellent talker)
The Mongolian Stomper
Big Van Vader
Post WWF Expansion Heels:
1997 Bret Hart
Lord Steven Regal
Austin and Pillman as the Hollywood Blondes
Al Snow in Smoky Mountain Wrestling
Sir Oliver Humperdink (his 82 work in Mid Atlantic is awesome)
Gary Hart (with Kabuki)