I'm voting for Unicorn Empire as a campaign (honestly, I play it instead of the single-player mode; it's just as good as Hammers of Fate for me), and also for Grand Frontier, Two Sisters, Artania – these are really excellent maps, the best among multiplayer and mission maps (excluding Dark Messiah). (And Two Sisters is the most hardcore!)
I'm voting for Unicorn Empire as a campaign (honestly, I play it instead of the single-player mode; it's just as good as Hammers of Fate for me), and also for Grand Frontier, Two Sisters, Artania – these are really excellent maps, the best among multiplayer and mission maps (excluding Dark Messiah). (And Two Sisters is the most hardcore!)