Tank Robes: With the right combo of spells you can become practically invincible, though your damage leaves alot to be desired, you can still kill with the overpowered stuff (rocks and ice melee, etc) and proves to be fun to soak up damage.
Support Robes: Very difficult to play, all your spells are lowered in damage because of your staff, and your melee is trash. (might have something secret, idk) Moreso made to armor up walk into a horde and then have your friend shoot magic at everything. This is probably the hardest to play in my opinion.
Rogue Robes: Very fun to play, and can be used to annoy your friends with pause, and harass a horde of orcs. Very fast, but squishy, tending to be easily killed if overwhelmed. If you increase your speed with the A,S,F combo, you can effectively run around and poison a horde of enemies before going somewhere safer to cast spells.
Though in the end, as the DLC states, these are party robes, and should only really be used in online play. I don't recommend using them single player unless you are seeking a challenge.