When was the last time each class (any spec) was considered to be (one of the) best? PvE only.
DK: 4.0 Unholy
Druid: Now Moonkin (borderline, if not then Cat/Resto in 3.1)
Mage: Now Fire
Warlock: Now Destro
Priest: Now Shadow
Paladin: 4.0 Holy,
Hunter: 4.0 Surv
Warrior: 3.3 Fury
Rogue: 3.2 Combat
Now Shaman? 2.4! THREE YEARS AGO!