In the 'ol days, being a wrestling 'good guy' or 'bad guy' was straightforward. You either act as cheerleader or party-pooper.
Hulk Hogan cheered his fans into a manic frenzy as his music repeated on and on. Bret Hart and the early Hart Foundation were heels who enjoyed destroying opponents.
At some point, a light went on in the wrestling community and the roles of heels and faces changed to the point of switching places. Hollywood long ago had the concept of dirty good guys and smooth bad guys. It was inevitable for wrestling to catch up.
Hulk Hogan now became 'Hollywood' dressed in black and 'The Hitman' Bret Hart became a fan favorite.
If a wrestler is ill-suited at being a face, the fans will boo said wrestler into oblivion despite their good guy attitude(ie Rocky Maiavia, Cena, Batista). If one is ill-suited as a heel, the fans will remain silent even if wrestler had fire blazing out of all their bodily orifices like a firework(but come to think of it, THAT might work).
Thus, today's fans want faces who don't care most times and just tend to go off(Stone Cold, Kofi Kingston recently). They want heels who show emotion, value, and sense; despite how misdirected those emotions, values, and senses may be.
Edge's raunchy reputation and methods of attaining titles validate this. It's interesting to see what those cold voices in Orton's head will tell him to do.
A matchup of these personalities will always be historic.
Few wrestlers are not bound by this reasoning. Rey Mysterio has always been a fan favorite in the WWE and is known for hyping up the crowd. Evan Bourne is a face's face full of smiles and fist pumps. A unique style of wrestling can keep fans happy with a goody-two-shoes face.
Now let's suppose we were to line up current wrestlers to be judged in front of a reality show style panel of judges. Each wrestler to be given the fate of where they stand. Now remember, most if not all those criticisms are controversial but all have some merit of truth. Here is a sample of how it would go down:
Carlito: He's tried both sides of the locker room but hasn't caught on to the upper tier so far. Reasoning says his apple spitting and short temper should make him an interesting face.
Chris Masters: His iron-clad Masterlock move(Full Nelson) could have made him interesting either way. Reasoning says be a face who won't hesitate to lock in one of the best and most believable finishers in wrestling.
Santino Marella: His sense of humor wouldn't make sense for a heel. The Rock is one of the only people who could make you laugh while cheating and being a cowardly heel. Reasoning says finding a way to be a heel is the way to become a serious contender.
Charlie Haas: Fans have been waiting for the true Charlie Haas ever since the stable days with Benjamin and Kurt Angle. There's nothing about him that says 'heel', so reasoning says find an interesting 'bad guy' persona so that he can join the title hunt.
Kane: A whole lot about him says 'heel', so reasoning says for him to become a face again. Many on the B/R have stated that they want the mask back. With the mask, he becomes more unpredictable but the only certain thing is that whenever he comes down the ramp, he's bringin' the hurt.
Gregory Helms: The Hurricane was hot a few years back and has been far from the main event scene since. Reasoning says that since he's not an overpowering presence, he should turn heel. TNA would be able to find a program for him (similar to Eric Young or Christopher Daniels), but is the WWE willing to do the same?
Shelton Benjamin: Benjamin's stock has peaked a few times but has yet to become a steady 'Blue Chipper'. In-ring abilities notwithstanding, the fans seem unsure what to make of Benjamin. Reasoning says to turn a good athlete heel. Even though the gold hair was a better fit for DC or Marvel, he should've used his in-ring ablities to help convince opponents to relinquish their gold.
I used Jericho's picture because he's able to be a cerebral heel as well as a 'loose nut' face.
DISCLAIMER: The content above is not guaranteed to turn a so-so locker room into a hall of fame...but it is a start...