The performance life of your air gun’s valve and seals depends heavily on the cleanliness of the CO2 you’re using as well as the type of seal the cylinder creates against your airgun’s o-ring. Dirty CO2 can cause diminished velocities and equate to fewer shots per cylinder.
There are several brands of cartridges (or capsules) to choose from and without being able to see inside of each capsule, it is impossible to know which brand or brands offer the cleanest CO2 and are of the best quality. Cartridges also come from various manufacturers and countries, all of which have differing standards of quality control. Each capsule has to conform to size, weight and temperature threshold specifications, but there are no regulations governing the cleanliness of the CO2 or the cartridge, so it is hard to know which is the best without testing each and every one – you could go through several o-rings and destroy a valve or two before figuring out which is best.