Heart of praxic fire is a must. Sunsinger is best in pve because of the self res and grenade spamming. Definitely level that up first. I also prefer the grenade that splits and hits multiple enemies because it allows for enemies behind walls to be killed. For pvp, void walker is best. Nova bomb gets more kills than radiance. I prefer the scatter grenade because of the area of effect and guaranteed kill if it hits. Overall, choose the class that suits your play style (pve or pvp). Edit: Forgot to recommend scorch melee for sunsinger and energy drain for void walker.