[ComTrav]

You'll find MA Ulm is a little contreversial on these boards; it seems to be a "love it/hate it" nation. It's fine for SP, though.

For SP, when I was just learning the game, here are some nations I found useful:
-Any country with strong national troops is more amenable to newbies imo. Countries with weak national troops that rely heavily on mages/commanders/special summons can be harder to get working (Agartha, Bandar Log, etc.)
-Since you mentioned flyers, I figured I'd mention Caelum, where almost everything flies. EA Caelum is great to play around with high level evocations, too. When learning the game its easier to focus on one or two schools per game.
-However, when you're ready to play with LOTS of different magic, Tie'n Ch'i (I played EA) was very useful to me when learning the magic system, because of its ridiculous magic diversity. It has a solid troop selection, too. Maybe play your 3rd or 4th big SP game as TC, the amount of magic options available to them are overwhelming at first.
-Someone will mention Niefelheim, and its probably the best bet for a bless strategy. Take high bless, build frost giants, profit.