when I first got the game I played on dif 1 for a while but that wasn't really challenge. After I was done with fooling around and understood a lot of aspects of the game, I moved up to 7/7. I've been playing between 7 and 8 ever since, random AI types and I'm actually winning on 80 planet maps. So I'm moving up to 8/8 as standard in a while. I've noticed that AI types influence the difficulty much more than the difficulty itself. dif 8 easy types are pushovers, while some dif 7 hard AI types can give me serious braindamage.