Unless you have Sol, Cass is often better. Despite how nice resurrection sounds, it's a rather useless skill that's never used to full extent in a winning fight and in a losing one, only delays your loss. I've been playing from launch and her revival skill has never saved me from a losing battle even once.
While you can just put chaos magic on Andromeda, you can just toss a regenerate skill on Cass if you don't need a debuff, it's far more useful than Andromeda's revive and makes up the difference of their heals while still keeping chaos magic.