Forget using any AI Knight Enchanter an absoultely useless class, and also the Necromancer which is totally bugged. The AI simply cannot play them at all.
I say K/E is useless, because the Ai cannot play them properly at all. Personally I wouldn't either I have better things to do when playing as a caster than endlessly casting one spell.
Solas. Riftmage all points in Rift, are super awesome cool, when selecting direct control, combined with full Spirit. Some Ice Frost Grasp, Mana regen, he is now a real killing machine. I take him to every fight..
Every mage needs a full Spirit tree. Your later choice of which elementals to master afterwards. For the K/E focus ability Rejuvenation, and better barriers. Worth investing, using, some of the Knight Enchanter points. Disruption Feild top tier is quite useless.
Fire: Has the most damage bursts, but also alot of enemies are immune. Spec using a full Fire tree as every spell has massive damage potential.
Ice: is a good choice for better Mana Regen, and Frost Grasp. Fade Step can be more trouble then its worth, forget about top tiers Ice Wall, Blizzard, and Ice Mines.
Lightning: Barrage, Chain Lightning, are really good damage. Static Feild, Lightning Bolt, top tiers are mostly useless, although some of the abilities around those skills are quite useful..