Marktest is leading in Top 10K Sites and Top 100K Sites.
Observer has better usage coverage in more websites categories. Including Business & Industry, Computer & Electronics, Arts & Entertainment, People & Society and 26 other categories.
Marktest is leading in Music & Audio, Religion & Spirituality and Soccer.
Observer is leading in most countries, including United States, Russia, France, United Kingdom and 9 other countries.
Marktest hasn't got a lead over Observer in any country.