Adsense: Most successful ad sizes

https://support.google.com/adsense/answer/17955?hl=en
336x280 Large Rectangle, the 300x250 Medium Rectangle, the 728x90 Leaderboard, and the 160x600 Wide Skyscraper

Ad sizes available for mobile ads
Text ads:
Mobile leaderboard (320x50)
Large mobile banner (320x100)
Small square (200x200)
Square (250x250)
Medium rectangle (300x250)
Image ads:

Mobile leaderboard (320x50)
Large mobile banner (320x100)
To help increase competition for the 320x100 ad size, we allow 320x50 display ads to appear within this format. When this happens, the smaller ad will be centered vertically within the larger ad unit.
Small square (200x200)
Square (250x250)
Medium rectangle (300x250)