Since you're mentioning seasons, I'll assume pvp is a consideration.

I had a blast with a Hunter in solo (one-toon) pvp (battleground), in Classic Warcraft.
Similar fun with a Mut/Prep rogue in Wrath of the Lich King.

Mages are the current OP class in battlegrounds, at least against every melee except a DK.
And have the tools to contribute in PvE as well.
Not sure if they'll get nerfed down to the ground next, or not.