Ahhh...the things people say behind the anonymity of the internet.
I've been door-to-door. No one does any of this BS that people claim to do here (aggression, pranks, etc.). Most people are polite, less than 1% are rude. No one gets off that great line they've always wanted to say. People are rarely "aggressive" when they aren't in their War-Craft clan. Dogs do nothing (doesn't anyone realize this yet?).
In real life your mom answers the door because you can't hear the doorbell in your "apartment" in your parents basement. (or in some sad cases, your soon-to-be ex-wife/ex-girlfriend answers the door because you're in the basement playing War-Craft, all day, without a job, paying for your monthly subscription from your unemployment check! Seriously?!?!)
For the less than 1% here who actually have their own place (sorry, not you guys with "roommates"), the best way is to either be polite and tell them you're not interested, or just don't answer the door.
To be honest, the once in a year that someone actually does something crazy (chase you with a hammer, girl answering door naked, etc.) you will probably make those guys day, and they will re-live those stupid antics to their fellow door-to-door acquaintances. But unfortunately, people are generally nice and polite when a stranger knocks on their door.
Edit: Not JW. Did the LDS Mission for two years a long time ago. Sold vacuums door-to-door for a summer in College...in Utah of all places...