My favorite location would be Jacobstown. Probably because of the sceneric look of it it. But the whole place is so awsome and stand out from all the other locations. I also love the road on the way up to Jacobstown. The one thing that I also found very fantastic about Jacobstown was the friendly super mutants, especially Marcus which I find as an outstanding character. As I am very used to play fallout 3 I was first very amazed by the friendly super mutants. As a short summary of Jacobstown is that it′s propably one of the most outstanding places in FNV when it comes to the atmospheric feeling and the characters which is living there. But it has it flaws, there isn′t much to do there and there is not any particularly good loot there.
And when it comes to the best vault I would say vault 11. The place had quite a mysterious and intresting story that made the whole vault outstanding in it′s own way. The best part must be the end of the vault under the vault overseers office. Im not going to give any spoilers yet but I would recommend any who is intrested in a mystical vault to take a look.
I only made a poll too the vaults. I leave the location as a more free topic