Water:
Ice Shard/Piercing Ice Shard for strong dps with in-built cc.
Rain for putting out fires/characters on fire.
Minor Heal/Strong Regenerate for excellent Healing.
Ice Elemental for a summon with CC built in.
Air:
Blitz Bolt/Lightning Strike for strong dps with in-built cc.
Air Elemental is a later summon than most (level 13) and no stronger than others.
Teleportation is great to move enemies/barrels about to set up combos.
Tornado at level 10 clears the board so it's safe for Madora to get across.
I assume your friend took Lone Wolf so you've only got 3 characters, in which case Water is more important as you want at least one person who can heal (ideally 2 is better).