Disclaimer: All my information about pepper spray is second-hand, mostly from the web. In other words, I'm no subject area expert. Below are just some thoughts.

I looked into pepper spray sometime ago as a possible aid in an active shooter situation. At the end, I decided that it was totally inadequate for that. I made a post with a preliminary list of the varieties I looked into, including projectile balls and projectile gel (guess this falls under your "other" category):

http://forums.equipped.org/ubbthreads.php?ubb=showflat&Main=15442&Number=210039#Post210039

As for your question, I am inclined towards the projectile balls or gel. Range is better. Cross-breeze doesn't affect it as much. Leave less peppery residue in the air. There is also the additional impact on the target's face. The main problem is that you usually need a gas-powered device to shoot the pepper ball/gel. So size is a problem. The other problem is that aiming may be more difficult, especially at the outer reach of its range. Stream can be affected too much by the wind. The range is more limited. On the other hand, this is what the police carries, and maybe there is a good reason (other than a canister fits on their belt more easily than a gas pistol). Fog seems more suitable for police work, controlling crowds and such. Not sure how it can be used for self-defense.

Since then, I have handled the Kimber PepperBlaster II (http://www.pepperblaster.com/). It seems like a nifty idea, even though it has only two shots. You can read the website for specifics on range, composition, etc. But let me tell you, even though it's shaped sort of like a gun, with front and rear sights, hitting anything under stress would be a bit of a challenge. There isn't that much for the hand to grab on to (your ring finger and pinky may hang off), and the distance between the sights just isn't much.

The worst thing for me is that for almost any brand/variety of pepper spray, you will be able to find a Youtube video in which the test subject takes a while to be affected. Afterwards they all complain about how terrible it was, but they all could have shot/stabbed/hit you over the head with a bat if it were a real defensive situation. For other test subjects, the spray can work quite fast. So this inconsistency worries me. If you want to carry a pepper spray, you'd better get ready to fight hand-to-hand, possibly against an armed assailant before the effect of the spray kicks in.

The stronger brands (Fox Labs, Sabre, Vexor, etc.) may have the additional problem that they're so strong that approaching or being near the "receiver" of the spray may become difficult. A guy reports that after he used a pepper spray on an assailant, the police came. They refused to take the bad guy to the station. Why? They didn't want to be in the same car with him. They made the good citizen who just defended himself drive the perp to the station. He says that he was crying the whole way from the residue spray emanating from the perp's face. Of course, this is almost a luxury problem as far as I am concerned, if the spray succeeds in saving me.

Da Bing