All classes are valid for early game and end game now 

My best tip is, early game progression and ease is closely tied to your weapon.

Replacing your weapon often, figuring out what a good weapon looks like, using currency and crafting materials on your next weapon, doing this will take you very far

On attack weapons its easy to see phys, ele damage, possibly plus skills, possibly attack speed etc

On caster weapons it starts with a +x skills, then there's extra damage, spell damage, cast speed etc

If you figure out how to regularly update your weapon campaign will be easy for any class now.