I find New Vegas was a lot more memorable, interesting and funnier, and the plot was much better with more choices available to the player. I've not played Fallout 3 since it came out granted, but I don't remember many characters from it apart from Three Dog, Dogmeat and the guy that wanted to blow up Megaton. Whereas with New Vegas you've got Mr House, Caesar, Fantastic, Benny, Jason Bright, Lily and more. The DLC was also substantially better.