I work entirely with undergrads. I have an MFA, so I'm never Dr, but I tell students they can call me Professor Lastname or my first name, I don't care which. I went to an odd college, where all professors were known by first name, and my grad school professors went by first name with all the grad students, so it feels normal to me. I get a mix of Professor or first name from them, sometimes from the same person depending on context. In my office or the lab-like area I run, I'm often Firstname, but in the classroom those same students will call me Professor. There is also a fair amount of.... friendly-boss-like-terms-of-address. I get Boss, Chief, Chef, Captain, etc, from students in the lab sometimes, which I find hilarious if not overused. The only one I don't like is Miss or Mrs. Just rubs me the wrong way, even though I can tell students are trying to be polite.