I came across a website today claiming that centrifugal juicers destroy virtually all of the enzymes of the plant you are juicing: "What is extracted? Mainly WATER content. What happened to the enzymes and nutrients? They are still embedded in the pulp which was choppped up and little else was done to extract them into your juice" (Link).
The author didn't provide any specific data, so I searched for studies done on this subject. The most thorough research I found was a study performed by Dr. Michael Donaldson.
Here are the juicers he tested for enzyme retention:
Here are the results of the study:
When purchasing a juicer, another important factor to consider is cleanup time. Many people have found that centrifugal juicers are very easy to clean, which can increase the likelihood of daily juicing.
In conclusion, non-centrifugal juicers tend to preserve enzymes about 43% better than centrifugal juicers. That being said, both types of juicers are a good buy, because both provide juice that is rich in enzymes.