Out of any of the choices available, the Courier can easily be far and away the hands-down best choice for an actual leader, which is exactly what you need for directing a city-state. A nice-guy Courier, on the other hand, goes around fixing a wide variety of problems (up to and including settling the entire Legion/NCR war almost by himself), making alliances, and enforcing order without randomly punishing the innocent or uninvolved. Yeah, House and the NCR both deal with the locals out or pure necessity and would happily do away with many of them just for convenience in order to establish their idea of 'order'.
I imagine the companions could do a lot to help strengthen New Vegas' relationships with the families, Boomers, Enclave, maybe even the Brotherhood and Khans.
Even if not, you have Yes Man, plus all the folks you know. An accomplished Courier has made allies all over the area, and probably has skills relevant to running the city, like talking to people and fixing stuff. People keep saying this, but I don't understand it. I do not consider the Legion to be a serious option, nor the Courier - who is, Player Character status aside, profoundly unqualified to manage and rule an independent city-state. To me, the choice between House and NCR comes down to which you trust more: democracy, with all its familiar flaws, or a ( mostly) benevolent autocrat with a grand vision (and all the Old World hubris that led to the War).
