I can't tell you the distinct difference between the pedal's listed, but in my experience, each and every pedal has it's own unique sound. You'll just have to test some out at a local music store to see which one would work best for you.

A compressor "compresses" the sound to make the volume even....In other words, it raises the volume of quiet notes and lowers the volume of louder notes. Compressor's can be your best friend or your worst enemy.