Get them all, and you'll get all their endings. Check out the endings on the wiki and you can see what works best - it depends both on how you solve their personal quests and the Hoover Dam battle.
I ment the 4 endings as in who gets the dam House NCR Legion or u
If you mean who should you support, then the NCR, Mr. House and Caesar's Legion all do a bad job at running Vegas. If you want Vegas to be good, you should make a good karma character and work with Yes-Man.
Actually if you work for Yes Man you either end acting as Mr. House or the whole thing goes to hell because the securitrons can't keep order. The NCR and House both rule perfectly well in their own ways, and the Legion rules effectively, if not pleasantly. Just start resolving quests how you feel like and it'll point you to an ending.
Yes Man is the best, because you don't have to kill the Brotherhood, Boomers ETC. and you can have them help you, also if you upgrade the securitrons they can easily look after vegas, plus if you help your companions with all their quests you get a good ending, and if you dont know which companion to choose have all of them with the all companion glitch.
- You don't have to kill the Brotherhood, Boomers, Khans etc. with the NCR either. Only House and the Legion.