The 300×250 Ad Unit provides Publishers High CPM Rates
Across the globe and at Healthy Ads, the 300×250, also known as the medium rectangle, is the most requested ad unit by advertisers. For branding campaigns, the 300×250 generates the highest click through and engagement rates compared to other units, and is thus the strongest performing ad unit. We recommend publishers include the 300×250 placement in their advertising mix. Because of its dimensions, 300×250 placements are typically top left, middle left or within content.