If I have to choose one, my choice is Adytum. Since Vault Dweller helped the Blades to wipe the Regulators out of the Boneyard, I'm suprised the're in full power again. If gang could control the town then... i mean it could happen again.
South is pretty much controlled by ncr. No idea about necropolis but there's nothing but ruins there.
i am quessing that in the ruins there are the best battles
2162 May 10 Fallout 1 Ends: Vault Dweller returns to Vault 13, only to be told "you're a hero, and you have to leave." Some members of the Vault (led by Lydia, the head of the "return to the surface" faction, and including her supporters, Theresa and Lyle) follow soon afterwards.
2238Harold arrives in Gecko, and (with a lot of shaking of his head) he does his best to help the ghouls with the running of the Nuclear Power Plant
Yeah the battles might be great, but realistically, what would you fight over?