Most liked to least liked: Midak skyblasters, zamor sphere launchers, rocket launchers, rhotuka disk launchers, stud cannons, tohunga disk throwers, kanoka disk launchers, nynrah ghost blasters, cordak blasters, squid launchers.
Squid launchers were stupid, because they only worked properly if you loaded and fired it in less that one second. Even then they didn't always work. Cordak blasters didn't always fire either; they were more reliable underwater, but they were still terrible.
Midak Skyblasters are the best for their compactibility and the amount of ammo they hold for their size. I first got a Nynrah Ghost Blaster with Mistika Tahu, and I didn't like it because its maximum range for me was 3 feet. However, a few months ago I got Gorast off of Ebay. It had a really good seal between the missile and the barrel of the gun, so its range for me was 40+ feet.
Disk launchers were not that good after they were used over and over again, but the Rhotuka launchers were very good for their range. However, they weren't very accurate over long distances. The best of all the disk launchers was either the Slizer or Tohunga throwing arm. It had pretty good distance and accuracy.
The zamor sphere launchers was good, but the spheres fell out if you turned it over (this is for the inika type, with the extension). A fix for this is to remove the 4th sphere and insert two pieces onto the top plus section, as were used on the Rockoh-T3. This fix allows for the use of several of the inika extensions to be used on the launcher. You can add pieces onto the piraka version of the launcher, but you'll need to design it yourself in order to shoot upside down. A bohrok shield works very nicely to simply keep the sphere in.
The rocket launcher (exo-toa) was very good for its power, although Lego later updated both the launcher and the missile to be more streamlined and powerful. Unfortunately, they never used this version in a Bionicle set.
The stud cannons are cool-looking, small and compact; they also hold the most amount of ammo that shoots without needing to be refilled. However, they don't have the power needed to knock larger sets over; however, Bionicles could be taking over the Lego world and shooting minifigures.
Now, when will Bionicle use spring-loaded shooters? (the octagon-shaped cannon on Cole's Boulder Blaster is the best; they should do something like that for a titan or vehicle)