Monetization using Google’s Adsense is far trickier than you might have imagined. You might think that since Adsense is a Google product, then they would certainly be biased towards pages that carry such ads. However, in reality correlation studies have shown that the more space Adsense ads occupy on a page, the lower that page will tend to rank. Of course, this doesn’t mean that Google is picking on their own ad service, but that it is merely consistent with how search engines (and users) view paid links.
The logic behind this is very simple. People tend to shy away from pages that have too much paid ads, as too much paid ads displayed suggest a spammy site.
Since users and Google alike do not like too much paid links on a site, what you should be conscious of as a publisher is to walk the fine line between monetizing your site and having it be considered as nothing more than a haven of paid links with nothing more substantial to offer. You can do this by being strategic in the placement of ads so as to minimize the use of ads as much as possible, yet ensuring that they get maximum exposure. You should also at least put some effort into making sure that the ads harmonize with the page’s look, so that even as they stand out enough to draw the eye (and clicks), they won’t end up and eyesore.
In the end, whether you have Adsense on your site, or use another ad service, following the above advice will help you in the long run.