it depends on the area! if the area you drop leaflets in is saturated with cleaners already then you aren't going to get much back apart from the customers they dont want(bad payers, moaners etc) if they are desperate for a window cleaner you will get loads of calls.
I usually drop on a road i dont think there is anyone, i knock on a door where it looks like someone is in, ask if they have a cleaner, then post away.
But you are much more likely to get customers door knocking, the response is 100%!! YES or NO! And you will pick up far more than you ever would with a leaflet, think about how many leaflets you have responded too in your home, very few no doubt.
Ive never had a negative response knocking for window cleaning, people say we've got a cleaner/ we do our own, or yes we need a cleaner!