I have five mustards in my refrigerator right now, including my favorite, Maille's original Dijon, and a Chinese mustard.
I'm not anti-ketchup, not even opposed to it on hot dogs (yes, really, and yes I am from Chicago). I just find that I hardly use ketchup. I just keep it around for other people.
I do like mayo with fries, but then, that's probably because I'm not big on ketchup. Mustard with fries, though ... that's something I have to try!