The basic banner ad unit is still the most popular with consumers.
A recent survey shows that people prefer banner ads that run in or around content rather than ads that cover-up content and interrupt viewing. (Dynamic Logic's AdReaction research)
The Research asked people's feelings on the major on-line ads formats.
The four best tolerated Web bad format are:
3) Pop-in Between Ads/Interstitials
4) Ads with Audio
No surprise here, people prefer the less intrusive format over the intrusive ones according to the research. Research also indicates preference for ads that pop in between Web pages (Interstitials) over the pop-up ads, which are the least liked and appear at the bottom of the list.
"It may be that consumers are more willing to tolerate advertisements when they are perceived to be around or in between content as opposed to feeling that the content is being blocked by the ads," says the Dynamic Logic study. "It is a subtle, but perhaps significant perceptual difference that impacts consumers, acceptance of the formats."
There is some evidence which would lead you to believe that pop-ups or pop-unders could be better tolerated if frequency was kept down. People have more tolerance for the pop-under, but not by much because the pop-under seems to trigger multiple openings of ads, which then must be closed before proceeding.
There are indications from this study that suggest people might be willing to accept approximately two pop-ups per hour in trade for free content.
Audio/video ads even though they're still fairly new, it's worth noting that they ranked at the middle of the pack. Which I believe suggests that improvements in the technology has made the video-like experience more attractive to viewers, and I think we'll see advertisers starting to deploy TV like ads more often online.
However there is a drawback, it seems these video/audio ads draw unwanted attention from management while employees view these ads at work. So now some publishers require that the audio side of these ads by default are off with an opt on feature.
Dynamic Logic says this type of Web advertising is gaining interest from both the advertiser side and to some degree, from the consumer side. It may be that TV-like Web ads bring an entertainment, humor and drama value to Web advertising, which increases consumers' interests.