Welcome to the forums! Green gas and propane are the same, fyi. Propane just doesn't have any lubricant added to it, which green gas does, plus propane has this smell... You kinda have to get used to it lol. For CO2, it is a higher pressure gas, so it shoots harder, but it also wears on guns faster, plus you have to get those little CO2 canisters and what not. I personally like running propane. And the last match that I went to at Vanguard was pretty nice, but that was 2 years ago I think lol.