The thing for me is that I just test as many classes/specs as I can before each expac to decide what I want to play and base my decision purely on gameplay not numbers… So in reality I always like my class/spec because that’s the reason I picked it.
Some notably fun specs I’ve played over the years are:
Cata: Survival Hunter.
MOP: Destro lock, Resto Druid, Holy Paladin, Balance Druid.
WoD: (no idea, didn’t play)
Legion: Disc Priest, WW monk, Resto Druid.
BFA: Disc Priest.