Let's start from the assumption that NCR wins the Mojave campaign.
At this point I guess that a territory so vast and important (for position, cities, resources) must have its own representative in the NCR senate (I actually don't know if NCR is a bicameral system, but chief Hanlon can become senator for Redding). So... who's gonna go among the "great and the good" of the republic? I am eager to hear you out
Personally I think that the choice would be initially restricted among the strip chiefs (I would put them on top given their wealth in the major Mojave city). Now, the omertas conspired with Caesar, the white gloves are involved in the abduction and potential consumption of a powerful cattle baron (which is bad in politics I am told). This leaves us with Swank since the NCR did not seem too involved with the whole platinum chip mcguffin. Hilarious, given that his rise to power would have been jumpstarted by his boss ambition.
On a "second tier" I put now other than the King himself. If you factor New Vegas as a whole electoral college, I guess he can rack up a lot of consensus if a treaty with NCR is struck.
The courier in the end is bit of a wild card. They could well be senator based on the individual courier one plays. Personally I cannot imagine my character strung up behind a desk/on a throne. But going by qualities alone I guess they would be the best pick
So, you have it. Let's start the debate and remember, Mojave, "No taxation without representation!"