Though, there are some other ad networks out there, but Google Adsense is so far the best. It is world’s largest ad networking site. So, the influence is more.
The other ad networks are not as popular, so the purpose gets spoiled. The motive of flashing an ad is to reach to the maximum number of viewers. Adsense works the best in this aspect. Though, it is difficult for any site to get an approval from Google, but if you could manage, Adsense will pay you back more than any other network.