Google has announced that they are now going to use the best performing text size for AdSense ads which are on default settings.
Today, we’re announcing an exciting improvement to our default font settings, which will optimize your ad units for your unique site and users. For each ad unit that’s set to show the default font face and font size, our system will now automatically select and show the best-performing option. This best-performing option will depend on a variety of factors, including the user’s viewing environment (operating system, browser) and the ad unit itself (language, size, number of ads, etc). We’ve tested the effects of these factors on our AdSense fonts and incorporated the best combinations into our default font settings. Our aim with this update is to help improve ad performance on your site by automatically applying optimal font settings to your ad units.
If the user has customized any of the text settings, Google would continue to honor them. It might be a good idea to revisit the settings and see if they need any changes!