Dry powder works FAR better, and the canister is much lighter to carry.
As a former firefighter, I can tell you that one breath full of powder WILL stop you right there. BUT the masks these cretins tend to wear will inhibit powder as a deterrent. CO2 will not stop, just perhaps surprise an assailant ... unless you strike them with the metal canister.
The mask is a sign of intent to engage in criminal activity. If near enough to one of them, rip it off and have your partner take a photo or video. Oh- wait; then you will be charged with assault. It's always SOMETHING!