Meta http-equiv
16,540,472 websites

Meta http-equiv is free to use

http://www.w3schools.com/tags/att_meta_http_equiv.asp

The http-equiv attribute provides an HTTP header for the information/value of the content attribute. The http-equiv attribute can be used to simulate an HTTP response header.

VS

X-UA-Compatible
11,141,235 websites

X-UA-Compatible is free to use

http://blogs.msdn.com/ie/archive/2008/06/10/introducing-ie-emulateie7.aspx

Allows a website to define how a page is rendered in Internet Explorer 8, allowing a website to decide to use IE7 style rendering over IE8 rendering.

Market Share by Top Websites

1 Meta http-equiv is leading in Top 10K Sites, Top 100K Sites, Top 1M Sites and The Entire Web.

2 In terms of market share, X-UA-Compatible is clearly lagging behind, losing to Meta http-equiv in all segments.

Websites Categories

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

2 X-UA-Compatible hasn't got a lead over Meta http-equiv in any websites category.

Geography

1 Meta http-equiv is leading in most countries, including United States, Japan, China, Russia and 162 other countries.

2 X-UA-Compatible hasn't got a lead over Meta http-equiv in any country.