I'm a light sleeper, but generally I like a fan blowing, and either the heat/ac running. Sirens and diesel engines make me sleep like a baby (blame it on years in emergency services and living in a medical center).
Since moving to China, I need noise to sleep. It really makes people a little unhappy when they sleep over that I have to turn on something. I am used to the squelching of bad brakes on big trucks and sleep right through them!
We both prefer some sort of white noise - a fan, air purifier, something. When I go out of town or house sit, it can be really difficult to fall asleep in the utter silence! I'll often fall asleep watching a DVD or Netflix in those situations.
Silence. I need silence. I'm a speshul snowflake sleeper. I don't know what I'm going to do when my son and his pregnant girlfriend move back home this summer. I'll have to learn to sleep to the sound of rain with my sleepphones.
I prefer no noise, nature sounds like light rain splattering on the window (or crickets chipring), or just something like a fan going but my mother needs the TV on to get decent sleep for some odd reason.
My first instinct was "complete silence" but actually that's not true. I prefer to have SOME noise in the background, but it has to be something consistent and fairly quiet, like a fan or heater. I can still sleep with complete silence, but it's just better to have that slight noise. No matter how tired I am, I CANNOT sleep with music or the TV on.