Some really good arguements here, and I have to agrre with most, so my thought is break it down to catagories (before people moan, I am an 80's kid, so I take the era 85 - 2000) I have heard and read all about Bruno, Andre, Arn etc, but not seen them, so am not including them. I do respect their legacies though, so anyone who argues for them, fair play. Here we go -
Best mic work - The Rock. Hands down the greatest to ever give a promo in wrestling. Some wrestlers are gifted on the mic (piper, savage, flair, jericho etc) but The Rock was something else. He could give a promo on quantum physics and be entertaining!
Best crossover appeal - Hogan. As mentioned several times, you ask anyone in any variation of a civilised culture who is Hulk Hogan, they will say a wrestler. Ask anyone to name 1 wrestler, they name Hulk. Whilst my opinion of hulk is low (never a fan) I do respect that he is THE most well known wrestler ever. He was in the right place, right time, with the right mindset to take the bull by the horns and appeal to almost everyone.
Best big man - Undertaker. Agile, powerful, intimidating. Many have tried to imitate him, a few get somewhere in the vicinity, but no one really gets close. 20 years of destruction (I know its his gimmick) but his gimmick could so easily have failed circa 96 when cartoon gimmicks started being rejected by fans. He took it to a new level then, kept evolving, and now is quite possibly one of the most respected and loved wrestlers in history. As someone in another thread said - "The undertaker could chokeslam a baby and get a face reaction". That shows how highly he is held in regard.
Finally, best technician - I've just got to go with Bret Hart. Accomplished amateur wrestler, solid mic work (not great, but could give a steady promo), good look, but in the ring, there was no one around at the time that could hold a torch to him. In Vince McMahon's own words (post screwjob, pre make up) "Bret was in a class all by himself when it came to telling a story in the ring". He could put on a match with ANYONE and make it amazing. Austin, Mr Perfect (although curt would be (or certainly should be) in anyones top 5 technicians as well) Taker, Piper, Flair, Yokozuna, Not to mention the incredible match with The British Bulldog at SS92, and of course HBK. I think the greatest match to never happen would be Bret (circa 1992) v Kurt Angle (circa 2000). Both were just raising their game to the highest level, going higher than anyone else were capable of in terms of skill, timing, and in ring mechanics.
Those are my opinions, for me, Bret comes out as the greatest all rounder.
Honorable mentions for Andre, Arn, Ric, Perfect, Ted Dibiase snr, Piper, Sting and HBK (although I think HBK's game was raised massively thanks to Bret making him raise it to try to be on a similar level to the Hitman) Too many legends to pick a single one, but, gun to my head I say the Hitman.