As per Google Adsense help section, it is the wider ad size that perform better as wider size of ad has better visuals and reader friendly. Readers can read wider size ads better than any other sizes. There are many sizes of Adsense ads available such as 336×280, 300×250, 728×90,300×600, 160×600, 468×60 and many more.
As per Google Adsense following ad size are most effective in terms of click rate –
You can watch the video below to learn more on increasing income through Adsense, ad sizes and placement.
We have made some split testing between ad sizes and number clicks obtained and results are displayed below:
Taking Full Banner 468×60 as 100% OR as base for comparison
Micro Bar (88×31)
Button 2 (120×60)
Vertical Banner (120×240)
Button 1 (120×90)
Square Button (125×125)
Leader board (728×90)
Sky Scraper (120×600)
Half Scraper (234×60)
Wide Skyscraper (160×600)
Medium Rectangle (300×250)
Large Rectangle (336×280)
Half Page Ads
From above comparison you can understand that which ad performs better. But placements of ads are very important. Like, you cannot put Wide Skyscraper (160×600) where Rectangle size of ad is required. Do not put Wide Skyscraper (160×600) before content (after title).
You can test Large Rectangle (336×280) in place of Medium Rectangle (300×250) ads in your site and see which is performing better.