Here are the top ten film festivals in the United States of America, per Brooks Institute web page. More detailed information and links are on the web page.
10. San Diego Film Festival
9. Cucalorus Film Festival
8. L.A. Comedy Shorts Film Festival
7. Chicago International Film Festival
6. San Francisco International Film Festival
5. Nashville Film Festival
4. Tribeca Film Festival
3. New York Film Festival
2. Seattle International Film Festival
1. Sundance Film Festival
http://www.brooks.edu/articles/top-10-film-festivals.asp