Man, I'm not sure. I'll tell you the fun things I like about both, however. Including some non AoE.
Druids:
Note: This is coming from a Balance Druid spec. Some moves are talented.
Mages:
- Typhoon: Large frontal AoE. Goes a good distance, does decent damage when stacked, knocks enemies back and slows movement for a bit. Awesome when followed up with...
- Hurricane: If you can get mouse broadcasting to work (I use HKN), this is a pretty powerful spell. If they are slowed at all when you cast this, they're basically dead. haha.
- Starfall: This is a talented balance ability. It rocks. Casts 20 stars that hit enemies within 30+ yards. On top of that, when the star hits, it splashes over 5 yards. You cast this, run around in a circle, and all of a sudden, they're all taking tons of damage. If you take on a particularly large group of monsters, it's no big deal. Just do a Typhoon near the beginning, and that'll soften up a lot of the monsters first, letting the extra stars attacks other players. 100 stars total when cast by all four players. There are Kill X number of Y quests where I can fly in, drop this spell, and by the time it's done, I've completed the quest. The Grizzly Hills PvP dailies come to mind. No one comes to attack you when they hear 10+ local defense alerts within the span of a few seconds. haha :P
- Treants: Not really AoE, but definitely worth noting. Treants cause so much confusion that it gives you time to get off that Hurricane spell, or any other AoE. People freak out when they see 15 trees attacking them.
- Moonfire and Insect Swarm: Provides 10 dots when using 5 druids. While not as awesome as Warlock DoTs, 10 DoTs are nothing to scoff at. Great for dotting up a few guys before moving on to more prized targets (Especially if they're running away)
- Tranquility: x5, Need I say more. Awesome raid-wide heal for downing AV bosses and such.
Note: This is coming from a Fire Mage spec. Some moves are talented.
So there's a lot of fun in either of them. Druids offer more survivability and utility. Level both for sure. Maybe just take turns. one week on one, one week on the other. Will help with your rested exp, too.
- Frost Nova: Good "Oh Crap" move. Keeps the enemies off of you if they get too close. Has a lame cooldown, but throw it into a cast sequence with your other mages, and it should generally be ready to go when you need it.
- Ice Lance: Instant cast damage spell with no cool down. Awesome! Damage is pretty weak. Damage x5 is less weak. Awesome spell to spam on a target you're chancing, or while on the move in general. There were many times I'd be chasing an enemy up a bunker, or tower, just spamming this spell. It's also fun to peg people as they try to run past you on mounts, if you find a nice choke point. Frost Nova them first, and the damage is like doubled, or tripled, or something. Way cool.
- Cone of Cold: Instant Cast. Decent conal AoE. Short cool down. Good for softening up targets that come into melee range before you bust out other spells.
- Dragon's Breath: Way more dangerous version of Cone of Cold. Does a lot more damage. Longer Cool Down. Disorients (I believe) Open up with this move when defending a horde tower, and it's basically game over. You can wipe up whatever is left with a few arcane explosions. This is talented under Fire, so may not work with those wanting to spec Ice. Cooldown can be manged in a cast sequence, filling in the other mages with Ice Lances, or something, to allow continuous DPS.
- Arcane Explosion: x5 this move is pretty deadly. Better if you softened them up with some other spells first (Fire Blast, Dragon's Breath, Arcane Explosion, Ice Lances). A good one to spam if on the run. You may go out in an exploding blaze of glory, but your teammates can finish off what's left.
- Flame Wave ?: The name is slipping me, but it's the talented fire AoE move, like Arcane Explosion, that also knocks targets back. This one is awesome. I have it worked into a cast sequence with Arcane Explosion. If I press Alt, they all Arcane, explosion, if I don't, one casts this spell, while the other four cast Arcane Explosion. You can just press this in a timely manner, and be particularly nasty. The knockback allows for lulz if knocking off cliffs, bridges, etc.
- Blizzard: Awesome spell. Even better if talented into the Ice Tree, I'm sure. I've no experiencing with it, myself, though. Make sure you can broadcast mouse clicks.
- Mirror Image: Haven't been able to test this one, myself, as I'm not 80, but copying images of yourself, when you already have five mages, seems to be about the coolest thing ever. I can't wait to test this.
Have fun!