Well, depends on the type of ads you want to display.
Google ads are what's known as "1-Click" ads - blocks of text that fit on the same page as your content, and are relevant to your content. Typically, Google has the highest bids and best CTR when it comes to 1-Click Ads, though this isn't true for all webmasters - bloggers, for example, love BlogAds (
www.blogads.com) because the ads tend to compliment the blog content better, thus increasing CTR.
The second type of ads are called 2-Click ads. This is when sponsored search results are displayed after one of your users does a search within your site.
Ok, imagine you have a search box on your site. A user performs a search there and is presented with a list of results. You show them sponsored results and maybe organic ones too. A user clicks on the sponsonsored results, and you get paid.
Which is better? Well, depends. Generally if a user is using your search box to perform a search, he's interested in the results and is likely to click on one of the ads. But why would he search on your site to begin with? Well, you may have specialized content and can provide a specialize search feed. Or you have put the search box in a convienient place for him. VERY few people click on the 1-Click ads (whatever google says) and most of us tend tend to ignore it.
If you're interested in putting a search box on your site and receiving sponsored search results that can earn you money
WHILE you are running Google AdSense, contact me and let me know.