I think you forgot brand ambassadors, people who actually wear your shirt because they love your service, want to promote it, and proudly do so. These ones are the best, because when asked what the company is or does, they'll know what to say and enthusiastically do so. I know bands who wear our shirts and absolutely tell people what Earbits is when asked, which you don't get from someone who says - I don't know, I just got this free shirt at a conference.