[Maltrease]

Well for one, mountain has more letters than dark. And thats pretty cool!

Another reason comes into play if you were actually to assault the fortress. A mountain citidel has much more defensive walls and shoots 32 arrows a turn.

I'm not sure what the dark citadel has... but it is not as good.

Frankly though... the number of letters is almost enough for me (if I ever chose anything besides a castle that is).