These days stove makers use a variety of gases and mixtures in their canisters. Years ago butane was the norm, but the stuff didn't perform well in temperatures at or below freezing, obviously an impediment to high-altitude or cold-weather use. Propane is great when it's cold. I used propane on a Denali climb several years ago, but it requires a beefy canister impractical for backpacking. Isobutane has also become popular of late; it's similar to butane but has a slightly different molecular arrangement that enables it to burn better in cool weather. It also helps maintain steady heat output when the canister nears empty.
Most canisters these days use a fuel mix that is 80 percent butane, 20 percent propane, a pretty good trade-off between butane's storability and propane's cold-weather performance. Gaz and MSR fall into this camp. Snowpeak and Primus add some isobutane to the mix, a gas that has slightly better cold-weather performance than butane, but these manufacturers use a similar ratio of butane-type gases to propane (I use the word "gas" loosely in the canisters these fuels are liquid). Coleman, interestingly, uses a 60:40 mix of butane to propane in the canisters for their X-type stoves, which explains why they're perhaps the best performing cold-weather canister-fuel stoves.
Aside from their cold-weather performance, butane, propane, and isobutane all have similar burn characteristics in temps above 40 degrees Fahrenheit or thereabouts. So for most summer camping, look for the stove that suits you best, and don't worry too much about the fuel mix.
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