for an example the best shaman currently alive would be thrall (in my opinion) Who is the best shaman,warrior,druid etc....
here is my list (I am an alliance fanboy, but tried to make this as unbiased as possibal)
druid: malfurian stormrage
mage: jannia proudmoore (would say rohinan but he died)
paladian: tirion fordring
death knight: darion morgrane
warrior: varian wrynn (many disagree, however this is my opinion)
priest: velen (you can see how much of an alliance fanboy I am XD)
hunter:.... I can't think of one
rouge:..... I cant think of one
monk: Chen Stormstout
I appologize for spelling errors! I am eager to hear your thoughts! please leave why you agree or disagree with my list!