Definitely leaflet then door knock.
Although it's more time consuming than pure doorknocking, it has a number of advantages. Some customers will ring on the strength of the leaflet alone, and those that don't will at least be 'warm' when you canvas them.
Also, it certainly makes me less nervous about doorknocking, as your spiel is really to the point 'Hi, I dropped this leaflet off in the week and just wanted to see if you'd like to have your windows cleaned'