Word of mouth, by far! When you click on a banner ad and land at a site, all you initially know about the site are the nifty little graphics in the banner. When you click on a search engine result and land at a site, all you initially know about the site is that it supposedly contains the keyword you entered in the search field. But with word of mouth, sites can come with a little or a whole lot of information attached to them. "I know the site owner" ... "Check me out on the site, I'm a regular contributor" ... etc etc - People don't just say "Visit this site" without giving more details about it.
It all depends how you maintain a good relationship and spread widely your contact sphere with your customers in addition to delivering them good product or service to get a WOM. I mean your good relationship will increase the vocal length of your customers otherwise they might whisper only. :rolleyes: