Dobgan is out. You're stuck with Obliheim.
To be honest, this is what my choice would have been. Dobgan was my #1 choice. They are, no joke, the best nation out of this entire pool. I will fight you if you claim otherwise. Of course, this lets me gush about them without worrying about giving away my secrets!
The Prince of the Sixth Whirlwind is a recruitable SC. All of them can cast Ironskin/Stoneskin. The A2s can cast Mistform, the D3s get to phoenix Pyre + Soul Vortex (always a treat), and the E2s, though less immediately abusable, can cast Rain of Stones turn 1. The F3s, well, they can't all be winners. (They are all sacred though.) They're amphibious, sailors, recuperate, and get 10 lightning resistance and 5 cold resistance out of the box, before path bonuses. And MR
20 out of the box, which is Void Being territory and past what pretenders get. These make the nation. They are
beautiful. But that's not all!
This guy is A2D1. The D1 doesn't matter much, except that it allows you to get Corpse Constructs. Corpse Constructs are excellent heavy-duty chaff for a very, very low cost, and you're going to want Construction anyways to get the items that really let you spam them. But the A2 is interesting - that's a hallmark for Thunderstrike spam. But you have no A3s to cast Storm!
Forge a Crystal Matrix, and now you do. But where do the communions come from?
Oh. Yes, that is a giant Witch Hunter for about 2/3 of the cost of a Witch Hunter, with recuperate. You can recruit these everywhere and they're not the cheapest communion fodder, but you only need two to storm, and they have good combat magic paths. Overall, you have your choice of thunderspam, Falling Fires (and other miscellaneous Fire spell) spam, Astral shenanigans, or Crystal Matrix shenanigans with Death, Air or Earth (from your cap-only mages), and all sorts of exciting crosspaths thereof.
But wait! There's more! Their priests reanimate! Your temples cost 200 extra gold, but that just means your infinite hordes of the dead are about 33% smaller (assuming you're spending the same amount on extra temples for indie priests), and 33% of too damn large to deal with is still too damn large to deal with, especially on top of the Fire Storms, thunderstrike spam, and Cloud Trapeze-ing SCs. You can also easily cast Solar Eclipse, and Darkness is in reach if you want it.
And wait! There's more! They get a 50g labrat, too. Not that you'll ever want to recruit one over your F2S1 turbocommunion fodder or A2D1 thunderspammers. They are an option, though.
Don't go yet! There's more! They have a troop roster which I have honestly never looked at. Who cares? Look at those mages again. Look, and weep, for you shall never find such beauty again. I guess you get a recruitable Fomorian King-chassis sacred and a bunch of decent human and Fomorian troops, but the mages are the draw. And they're one hell of a draw!
e: i guess they don't get blood magic for lategame though