'Tis correct, we have never aquainted!
Therefore Stuart, bottom line is: If you've got a descent marker and you play any tourney ball where it's a lot more important to have you ball velocity as high as possible without having to worry about firing hot - then go for compressed air or nitro as it's very reliable and constant.
If your more a rec baller with a more modest gun then you should be fine sticking with CO2 (which is actually liquid, not a gas - I assume your talking about CO2). An air system would, of course be a good upgrade no matter what, but not so important if your purely play recball.
Hope that helps