It completely depends what you're trying to accomplish. Banner ads work best for branding once a site is successful and established. They are pretty good at getting some word of mouth going as well. Text links work best to boost SEO. Having inbound text links will convince the search engines that your site is worth investigating - the more backlinks, the deeper the spiders will crawl and the more pages they'll index.
cscgal
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My post in this thread from 2005 (back when AdSense was a baby and buying text links wasn't considered so taboo) suggested that text links work because of their SEO benefit. I still think text links work, but now I'm talking about the AdSense kind ... contextual ads that can be much more tailored towards a particular page's content than banner ads ever could. Text ads work better because they tend to be more relevant.
cscgal
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