Mage for sure, although you don't really fit in the current meta of premades, the class itself is pretty fun, and not completely useless. It has good uses in arena as well, since frost mage adds good control, and that mages have hard cc and ranged interrupt at 19. (RIP, losing CS in Legion though...)
Also, being able to add that control in a WSG environment can really turn the tides. But yeah, in premades, you'll get shit on. At least from what I've been able to see from US premades and tournament play. Mage just doesn't really fit in at that level of play. Maybe I'm wrong on the premade / tournament stuff, since I don't have any personal experience to give
(EU is dead). But it's nontheless what I observe.
Fun in BG PuG's and arenas though.