Thrall
Winger
TBC was the best expansion by some distance. In Wotlk they casualised the game to much for my liking, it still had its fun moments though in Ulduar and Icc also not forgetting the most balanced arena has ever been.Tbh I'd say Wotlk was the worst expansion. It was the moment Blizzard gave up and let everyone have free high level gear. Pretty much everything after Uld was faceroll for anyone half decent at the game.
Nothing can compete with pre-nerf Kael'thas. Failing for 30 days then killing him on an off-night where half the raid was drunk was tremendous.
It was also the point where I re-evaluated my life and stopped playing.
Wotlk was still much better then Cata and MoP though.