Personally, I like to make an assessment of my feelings toward the favor done. If I feel put upon, I give an "mhmm" or "yup". My enthusiastic response is usually "no problem!"
"You're welcome" implies you can ask for favors anytime, day or night, and feels a bit too prostrate. I'll say it to some people, but it almost feels like an "I love you" type of response, and I reserve it for when I really mean it. I don't say the words "you're welcome" casually. I kind of say them like you would say something deeply truthful to someone
While we're at it, what's up with young people saying "bless you"? I kinda thought that one would have fallen off with people under 35