Korolev said:
Mordin.
I liked Mr. House quite a bit, but New Vegas was about exploring the wasteland, not so much the main story which was a bit short, and so Mr. House didn't have much dialogue or backstory (A rich smart man is a rich smart man, what else is there to him?). Also, I liked John Henry Eden better.
I thought Mr House had a good amount of backstory, infact he had way more backstory than Eden, especially considering Eden didn't technically have a back story, but he was one of the better "characters" in Fallout 3.
However, personally in Fallout: New Vegas my favourite character was Craig Boone, awesome voice and skills and a depressing past. Great companion.
John Marston was also a great character, very rich personality, philosophies, moral values and the like.