Nobody likes pop up ads. Everybody sees it as junk that appears without being requested. We always know that when we browse a website as a user.
We often forget that when we stand as the one designing a web. Some advertiser may pay good price to put pop up ad in our site. Or maybe worse, we give our brand/company site a pop up ad of our specific product or related brand.
Pop Up ad annoys visitor. Giving user pop up ad is like serving them something they hate, making them uncomfortable. They’ll leave our site with bad experience. We must respect all visitors. If they want to see something, they’ll browse. Don’t need to oversell anything.
Better keep the ad in the form of banner.