When I researched this subject before buying my juice, I found that the centrifugal juicers tend to oxygenate the juice because of the way the juice flys through the air inside the machine. Although I don't think this is a huge issue, it does begin to deteorate some of the enzymes.

All things considered, I found the Green Star to be the best. Here is a picture of mine:

My Green Star Juicer