AppNexus
1,380,787 websites

AppNexus offers both free and paid options

http://www.appnexus.com

AppNexus is the most advanced platform for buying real-time online advertising. AppNexus's clients include the largest ad networks and online advertisers. AppNexus offers a proprietary gateway to premier ad exchanges and ad inventory aggreg...

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Google Publisher Tag
545,414 websites

Google Publisher Tag is free to use

https://support.google.com/dfp_premium/topic/28788?hl=en&ref_topic=28149

Google Publisher Tag (GPT) is an ad tagging library with which you can dynamically build ad requests. GPT takes key details from you such as ad unit name, ad size, and custom targeting, builds the request, and displays the ad on web pages o...

Market Share by Top Websites

1 AppNexus is leading in Top 10K Sites, Top 100K Sites, Top 1M Sites and The Entire Web.

2 In terms of market share, Google Publisher Tag is clearly lagging behind, losing to AppNexus in all segments.

Websites Categories

1 AppNexus has better usage coverage in more websites categories. Including Arts & Entertainment, Science & Education, Computers Electronics & Technology, Games and 20 other categories.

2 Google Publisher Tag hasn't got a lead over AppNexus in any websites category.

Geography

1 AppNexus is leading in most countries, including United States, France, Russia, Taiwan and 160 other countries.

2 Google Publisher Tag is leading in Japan.