What are the best builds for companions?

[Porcelyn]

I make him a Battle mage for the passives, especially constant recovery.

[Ilyan]

For the new sidekick, Mirke, as a brawler, with a greatsword (ok ok THE whispers...), she's a demon, amazing. The damage she deals... just I can't believe.

[Ichthyic]

I'm making Aloth as pure Wizard. But i seems to make him tanky as i wanted him to cast meteor shower for the PL9. As good tips?

There are plenty of defensive spells in the illusion and enchantment schools to make aloth near untouchable, even if you make him an evoker instead of no subclass.

 

almost all of them are quick casting, and many are zero recovery.  you won't have a problem making him defensive enough so you can run into the middle of a group and nuke them.

 

with high int, those spells will last a while too.  plus, there are plenty of excellent potions in the game that can add to your armor and defenses.  there's no trick to this, it will be obvious as you start to play the game which spells to use and which potions to use.