[Edi]

Depends on your playstyle. Some nations suit some players better than others, for example, Ulm and Abysia are both nations that I like to play and fit me well.

In EA Vanheim and Helheim are good nations that have excellent line troops even without the sacreds, so you can try those. Ermor as well.

In MA, Ulm, Arco, Pythium, Ermor (but the communions and undead reanimation give it a bit of a spin, so a bit advanced to get the synergies going). Man is also a good choice, as is Marignon.

Try things, play around with them. DON'T start with EA or LA Mictlan or with the other tricksy nations unless they are really your style.