One of my all time favorite games. A very under rated game in my opinion.
The OSG rules are a little ambiguous on certain topics. I believe the AH and the COSI rules are essentially the same and clarify some of the COSI rules ambiguities. The AH/COSI rules are easier to read since there are numbered reference points. The OSG version of the game can be played using the AH/COSI rules.