Sacred Haven of Debauchery

But House, independence, and the NCR are more ambiguous choices than everything else in the fourth game. As for the Legion, it's impossible to seriously consider it as a viable option.
And overall, I agree. If Vegas had never been released, and there were only the third and fourth games, I would even say that the fourth game is a good one, because it fixed many of the shortcomings of the third, but unfortunately, Vegas set a certain quality standard that Bethesda will probably never be able to reach.