The Differences between Theurgists Pets
According to Anonymous who posted on Allakazam
Earth pets are tanks - they have more hit points, last longer, and melee the enemy. Ice pets prefer to cast - they stop a distance from the enemy and cast ice spells, doing dmg and rooting. Ice pets have less hit points and dont last as long. Air pets are a mix, they melee the enemy and cast stun every couple of secs.

I generally send one earth to tank, follow up with a ice to nuke, then send more earth or ice. If I gotta run, i use air.