If we assume that WoW will keep running forever, it's most probable that he/she hasn't been born yet.
Some of you are arguing that people that started in earlier expansions are somehow better than current players just because they were innovate and didn't have others to learn from.
This is almost like saying that scientists in the 1500-1700s were better than any current. Of course going by that logic Archimedes must be even better, and Thales even better than him again.
Point is that you might as well rename this poll to "What is the best color?", or "What is the best number?" - the results would be just as incoherent and diverse as it is now because it is totally subjective, and there will never truly be a way to decide who was the best player, and this goes for just about any sport.
One can even argue that in sports that are easily measureable (I.E 100m dash, weightlifting etc.), it's not fair to rate the current world record holder as the best of that sport of all time. Can you for example say that given the same equipment, and the knownledge of how the body works today that Usain Bolt is better than say Carl Lewis or Jesse Owens?
In closing, WoW during its tournament prime (2008-2010?), as far as I know always missed the dominating force that we can find in other sports, so it was difficult for the crowd to pick a favorite as a team could be dominating one tournament, and then be one of the first teams to get knocked out the next one. To me this proves that WoW has always been very unpredictable (RNG-based), and solidifies my opinion that all the players listed are of top class, but distinguishing between them is next to impossible (nothing is impossible?