I like: Rragar's Menagerie, Vloxen Excavations, Shards of Orr, Slaver's Exile.
Why I like Slaver's Exile: Big groups of enemies, strong dwarven groups which resurrect, create minions, overhex, crush you, and so on.
Vloxen Excavations: Two or three nice dwarven groups.
Shards of Orr: Nice damage and always blinded.
Rragar's Menagerie: I love crushing little Charrs.
That's why I voted for Rragar's Menagerie: You can kill hundreds of Charrs. I hate them.