I have been vounteering for the GABF for 10 years now and the Saturday members session is the best by far Unless you are looking for a frat party style session then I recommend friday or sat night sessions). As someone else noted, there are a lot of side events a lot not related to GABF, that are well worth the time to go see. there are also brews cruise and brewery tours where you a driven to different breweries. There is a lot to do in Denver and I hope you all have fun! I'll probaby be pouring your beers when you go. Cheers in advance!
P.S. I have a list of things to do in the area and places to eat that I gave to someone last year, if you would like it then PM me and I'll shoot it over to you.
"Sometimes when I reflect back on all the beer I drink I feel ashamed. Then I look into the glass and think about the workers in the brewery and all of their hopes and dreams. If I didn't drink this beer, they might be out of work and their dreams would be shattered. Then I say to myself, it is better that I drink this beer and let their dreams come true than be selfish and worry about my liver." --Jack Handey