I voted:
EA R'lyeh
MA R'lyeh
LA Argatha
EA R'lyeh because I love turning the Mind Lords and Aboleths into thugs. Honorable mentions (Pangaea, Niefelheim and Tir na n'Og)
MA R'lyeh because of the void gate.
LA Argatha because of the mages
.
I like all the vanilla nations except for a handful, so really I am voting on which ones I like right now. My taste will probably change again in a few weeks.