If Piper can't beat Edge. Well I'll be upset, I'll leave it at that.
My voting criteria is a big coctail of things depending on who is involved. It involved booking and kayfabe, but also quality, longevity, ring work, mic work and more, and then setting all of those things up against a time chart. The ratio of importance obviously ranges greatly through time. Mic work didn't really matter back in the 60s, but without it these days, you're not likely to get over. What got you over in one time period might not work in another, sticking Lou Thesz in 1999 WWF might make him flop, similarly with Jericho in 1967.
It's a careful combination of things, and the best people seem to do well all round throughout the categories. If someone is exceptionally good or bad in one particular category, though, it can carry them through. Ie someone like Benoit can do well in this tournament because of his ring work being so good even though his charisma was low for a big star. Comprende homies?