Form B, I was talking from personal experience and not generalising. 
Fair enough, but from my personal experience you can build a solid customer base from flyers.
The main advantage flyers have over door knocking is that the customer contacts you which (I am generalising) tends to mean that they were more inclined to want a window cleaning service. As opposed to someone who (again, generalising) you have switched the charm onto and convinced that they need your service.
I don't deny that you will probably pick up more quicker by knocking on doors. I just think it's silly to rule out a cheap and relatively easy alternative altogether.
This is exactly why i built up my whole business on leaflets.
The customer asks you, you are in control. I was in sales for years, and i know if someone approached me to buy/quote, i was in!!
Even now, i wait for people in the street or new neighbours in the street im cleaning to approach me, ill say morning etc, but will wait for them to ask me about window cleaning.
Yes it may take a bit longer, but ive built a real solid business up this way.....i still drop around 80k leaflets a year (use a company to deliver them), and am already outgrowing my 2nd van!!!
maybe door knock to get the cash flowing, then mass drops to get a solid base.