While I really dislike anyone knocking on my door to sell me something, regardless of what that thing is, I do have to admit...

Mormons are usually the least objectionable of all the door-knockers. They tend to be genuinely friendly (or at least are able to fake it really well), respectful, don't do the "hard sell", and when I tell them I'm not interested, they honor my statement and leave without trying to change my mind or guilt-trip me.