Google Adsense

Wider ads appeal to more visitors because they’re easier to
read. If something is easy to read, someone is more likely
to take the time to read everything rather than just glancing
at the first few words. However, it’s important to balance
your ads and the content on your pages. You’ll discover that
the way you think the ads should be for optimal CTR aren’t
always where they need to be. Monitor your ad placement
versus CTR and you’ll find the place and format that works
best on each page.