Medium rectangle (300 x 250) is the most used and recommended by Google ad for sidebars/laterals. Now the sidebar width is 300px and is not posible use this ad. Is possible do the sidebar a little more big?
(for example 320px - 300px + 10px margin)
- About Medium rectangle (300 x 250):
The sizes we've found to be the most effective are the 336x280 large rectangle, the 300x250 medium rectangle, the 728x90 leaderboard, the 300x600 half page, and on mobile the 320x100 large mobile banner.
Also known as a "medium rectangle". Tends to have more ad inventory available from advertisers, which can increase earnings when both text and image ads are enabled.