I had CO2, presumably for speed/weight. I carried two bottles. Last flat I had, I realized that:
1. I tried to get enough air in to limp home, but the leak was faster than I thought (ever happen to you?). So I patched it, but the patch was bad, and now I was out both bottles, with a flat tire. Still had patches left, and a spare tube if I could air it up.
2. I later weighed the (empty!) CO2 bottles/system against the Road Morph G. The Road Morph G was heaver. By 10 grams. I can live with that.
3. I realized that fiddling with the CO2 bottles--getting them situated in to the delivery mechanism--it took a non-negligible amount of time. I had to unscrew the carrier, insert the bottle, screw it back on to puncture...etc. Obviously this could be faster maybe with a better designed system, but the pump is grab and go. I think it took literally 60 seconds to air up my tires. I can live with that.
4. I compared the volume of the two systems. They're comparable. CO2 has an edge in that it's a neat little square package. But it has more "fiddly bits" to keep track of.

So it seemed a wash more or less, except my pump works as many times as I care for it to. So I switched back to the pump.

(I also sprung for Specialized Armadillos at the same time. I'd rather not flat at all of course.)