FO: I would deffinatly have to say one of the broken down vaults.
Either 15, once I had cleared it out. The Cathederal would be a good spot, once you had cleared out all the goo from the walls. Possibly the one in Necropolis too, once you make friends with the gouls and they start revitalising technology again, that would be good.
FO2: Screw a built town. I would get my hands on the two GECK's and build some kick ass city centeralised on the map. Near new reno possibly. That or hire in a cart load of jet junkies from new reno, redding and the den and have them clear up the Millitary base, perhaps hire in some Shi as gaurds, as soon as they start to turn into super mutants, out come the gauss rifles. Then once the base is operational upgrade it with the Geck... yeah.
That or Vault 13 / 15