This is a reallly broad topic considering that 99% of the wrestlers on the roster since the attitude era have been both a heel and a face.
Heels- Bret Hart and Hart Foundation before montreal screwjob-when they started the anti american thing, they were so over as heels, got amazing heel heat. Kane has always been much better as a heel, especially when he first came in as the Monster he was. Owen Hart during his I'm not a nugget days was a great heel. Taker during his Ministry of Darkness days was an amazing heel. Alot of people forget how good of a heel Farooq was during the Nation of Domination days. Of course Vince/Shane and Steph during McMahon Helmsley faction and Billion Dollar Princess. Kurt Angle was always an amazing heel. I feel HHH was always better as a heel by himself. Right to Censor got great heel heat as a faction. Brock Lesnar, CLB Christian, Jericho during all his different heel turns, JBL's character was always great also(he really did remind me of a JR Ewing type), Muhammad Hassan, Evolution as a group. Edge has also always been better as a heel as has Orton. The Dudley's I thought were always a better heel team when they were putting everyone through tables. Angle/Edge/Christian together. King Booker. MVP much better as heel. Then you gotta look at how great of heat of GM's got: Bischoff, Vicki, Heyman, Steph.
Faces- Austin was the ultimate Face and probably the greatest face ever. The Rock was great, Foley was amazing. Taker, HBK, DX, Goldberg, Hogan after he left the NWO was getting awesome crowd reactions, You might laugh at me for this, but The Oddities got huge pops as did Too Cool(Rikishi, Grandmaster Sexay, Scotty 2 Hotty), The Hardy's as a team, Jeff Hardy solo, Flair, Piper, RVD, Benoit, Y2J when he was making fun of Stephanie, EUGENE, APA, Eddie lying cheatin and stealin, Rey, Batista is a much better face then trying to be a monster heel, Santino, Hornswoggle, Evan Bourne, HHH although he's a much better heel, and of course Cena..