This time around I requested GAs (but don't waste time choosing the price, it will do it automatically if you pick GA). However, during the pre-sale, I chose 'best available', got in right away and was offered two GAs. Unfortunately I lost them due to account/password problems.
I think both can work, it's really a question of luck. The thing is I don't know if 'best available' is random or always go for GA first. Maybe we should give a call to Ticketmaster about that.