Yaaaay!
Gotta be House.
The entire game suggests that both NCR and Legion svcks, so it'd be weird if they were like "LOL NVM NCR WINS." Yes Man let's everyone live but also feels like a cop-out. House is just a cool, interesting character and it'd be a shame if they wrote him out of the Fallout universe right after he got here.
I'm sorry to stick my fat head in here, but I totally agree. I thought he was gonna be a bad guy but he's actually the only voice of reason, apart from the money obsession of course. I also recently found out that there are different 'kinds' of ending for him, so you don't necessarily have to feel bad about it. (I've only completed it three times, once for each main faction.)
And of course, it always helps that had he appeared as his younger self, I totally would.