Masticating juicers ensure that you get the maximum nutrition from your juices. The danger when juicing is that if you work the produce to hard or too fast the fast processing introduces oxygen. The oxygen very quickly gets to work on the juice and starts shortening the shelf and reducing the value off the juice.
A quality masticating juicer is designed to extract the juice slowly thus minimising the oxygen and heat inyroduced during the juicing process. This ensures you ae getting the best juice possible. In terms of brands there are some great juicers out there and the quality does tend to vary on price of course.