Magnuson makes positive displacement, ATI makes centrifugal, STS has a turbo kit for the 04, and they're currently working on the 05 and are pretty close to release.
When it comes to which people prefer, it's a very subjective topic. Some prefer the massive high-RPM horsepower of the centrifugal supercharger, some prefer the low-end torque and steady powerband of the positive displacement (my personal favorite) and some prefer the monster torque curve of a turbocharger. It really depends on what YOU want.