At the end of the day, word of mouth is probably the best that any single person can do. I'm always hoping for a magic bullet. Personally, I might get a buzz out of seeing an ad on my door, if only because it's an improvement over the zilch that I usually see.
I completely agree that a libertarian tip would leave a bigger impression on me than a door hanger. I think it's also really important to make some kind of concerted political effort though. It's an important part of the education process. I probably wouldn't be a libertarian today if Ron Paul...
At the Libertarian party website, they sell these "World's Smallest Political Quiz" door hangers for 5 cents apiece:
https://lpstore.org/product/door-hanger-quiz/
On the surface, this seems like a pretty ideal way to advertise your cause. I can't think of a cheaper way to get a message in front...