What Class Should I Do Next?

I’m almost done with my mage, so should I play on my level 77 warrior or on my level 45 assassin?

 

Honestly I'd go with your personal preference- which do you enjoy more? They're both fun classes :)

 

Level up your Assassin, since your Warrrior will hit the great XP dry spell of 80-95 real fast.

 

Assassin I have a general bias towards but I have been having loads of fun on warrior as of late.

 

As said above, just level the one you like more. If you don't care at all about which class you play as, I personally would level up the Warrior, since it's closer to endgame and you could get it there. Having two level 80ish classes and having to face the lategame grind twice in a row may feel a bit eh.