I know you said dungeons...

I found Ferals (but Boomkins would be the similar) to level extremely easily by questing.
Any of the kill quests are absurdly easy, with the massive DPS they have.

I didn't really bother with the Cat-Charge, Pounce, Ravage, Shred thing.
Just run up, or lead toon can Feral Faerie Fire.
And run the Mangle-Rake-Mangle-Mangle-Rip macro... no facing BS, and they blow my now more geared (including Conquest 2Handers) DK's away in the DPS department.
Sure cats are more fragile, but quest mobs go down in 1-2 seconds.

And any of the ground-spawn collections...
Park the toons in a central area, 100 feet into the air.
Fly them one at a time, getting as low as 5 feet into the air.
95% of the time, you can loot whatever while standing next to or between the legs of a mob without aggro.
Even if you get aggro, you can time when to start to loot to get the item.
If in danger, press spacebar and switch to another druid... the first will regen safely in the air.
If you're high enough and out of combat, have them all hit the low one with Rejuv and then re-Flight Form as you fall.
I did have epic flight on the team.

Druids level very quickly, via quests.