Till now Adsense ads were being displayed in random font size.Google today gave an option to set font size for Adsense ads.Adsense font style option was introduced before few days.
The ads are available in 4 different sizes.Adsense default (The old classic font size) , Small , Medium , Large.
You can choose for all units in your account or you can set font size for particular ad unit.
To change font setting for account go to My Account.Edit Ad Display Preference. Change font size and save settings.
To change font settings for an individual unit go to AdSense Setup —> Manage Ads.Then Edit code setting for the unit.
What you can do is if you have high traffic you can choose which font size is best for you.On large font you may feel sometimes that you are flashing that it’s an ad.
Good gift from Google.I am feeling lucky like premium Adsense publisher.