The most common juicers available on the market today, the ones that you see on late night television commercials and in department stores, are usually centrifugal juice extractors.
These types of juicers will use a sharp blade that spins at high revolutions to extract juice from fruits and vegetables by grinding them up and using centrifugal force to separate the juices.
A masticating juicer works very differently. This type of machine will grind, crush, and squeeze juice out of the fruits and vegetables you put into it.
Centrifugal juicers are usually quite a bit faster and do a really good job of extracting juice from fruits and some vegetables but they can struggle a bit with green leafy vegetables. The rapidly rotating blades chop up green leafy vegetables without extracting very much juice.
A masticating juicer will use an auger to push the vegetables through a screen, crushing and squeezing the juices out of the vegetables. When it comes to green leafy vegetables a masticating juicer is able to extract the juices far more effectively.
A masticating juicer will also be less noisy, less messy, and generally easier to clean as well. They do not make as much noise because they operate slowly and do not have a motor zipping along at thousands of RPMs. The lack of a rapidly rotating blade also reduces the amount of splattering, keeping things quite a bit cleaner.
Masticating juicers are usually more versatile machines as well. In addition to being able to effectively extract juice from vegetables that give centrifugal juicers of rough time, masticating units can also be used to make nut butter, pates, baby food, sauces etc.
If you have the need for speed a centrifugal juicer might be the right choice for you but a masticating juicer will usually do a better job and is a much more versatile machine.