If you can, do everything! I get a good return on leaflets 0.5% which more than pays for itself. Google adwords is ok (and pays for itself) but is just starting to get expensive so I'll cancel that for a while. Canvassing is good and cost nothing but your time. I have had good and bad customers from all three methods and they all have their pros and cons. I don't care which method is best, I just do the lot and as far as I'm concerned, it's all good, providing you do it correctly.
