Evan is useful mainly for one thing. Rune duration Link Skill. If you get it to level 120 at the very least and then leave it at that, not a bad idea. It's best to do burning on Evan to speed that up as much as possible if you want the most optimal training exp link combo.
As for what to do after that, that depends really on what link skills you need and what class you think will be fun. There's no right answer to which class is the most fun to play. That's something you'll have to find on your own as everyone has their own preferences on which classes they like the best. Watch a few videos on several classes though to get a good grasp on how they look.
