Finished leveling my rogue but I want a ranged char next and I think I’ve narrowed it down to fire mage or mm hunter mostly. I like all the specs of both, but any advice on which ranged to play for pvp this season?
Why mage? The class is pretty much only enjoyable if you’re very masochistic because you’ll get trained all the time.
Shadow priests or warlocks are much better ranged DPS than both mage and hunter.
But if you have to pick between mage or hunter, the hunter is probably the better pick, as it won’t take weeks to become efficient. Hunters don’t get interrupted. 
MM is probably less frustrating to play. Although, MM damage has been kind of weak. They did just get a buff. Probably depends on the type of pvp you want to play. In arena (3s) Mages seem only good with classes - Rogue - that can give them the opportunity to do anything.
I haven’t really seen any mages at 70 that do impactful damage. Not to say there weren’t competent mages, but in PvP they were essentially just little gnats that you occasionally focus when their CC starts to get on your nerves.
Hunter feels way better than mage against the current meta melee specs imo. You have tons of roots/snares/knockback/stun options though a lot of them are difficult to hit at range. You’ll still be a masochist for picking MM, but not quite as masochistic as mage mains right now.
Hunter all the way.
Hunter for sure