Bigger is better, right?  Except when something’s too big, people view it as obnoxious, and the object in question gets shunned.  So if you’re waffling between using medium and large AdSense rectangles, some new info supplied by Google may help straighten things out.

A post on the Inside AdSense blog states, “We took this question to our Optimization Team, who gave us insight into the strengths of each ad format.”  Use these tips as a guide, although of course, you should test stuff out on your site to make sure the general rule holds true.

Anyway, the post stated, “The 300×250 medium rectangle is a widely supported format that advertisers often use when designing their branding and rich media campaigns. Using this ad format and opting in to both text and image ads may generate more placement targeting opportunities, which will help drive up competition for your ad space and should lead to higher earnings over time.”

It also noted, “The 336×280 large rectangle tends to have a higher clickthrough rate due to its larger size.  It often performs well on text-heavy pages where it’s integrated into the content.”

Good luck using this info to your advantage.