Slow or fast
The name might be a little misleading, since slow juicers are not slow in the sense of a tortoise – they simply take fractionally longer to extract juice than fast juicers, the reason being they extract juice through a method of crushing and squeezing, rather than shredding food with a blade.
This teeny bit more time spent, combined with the lower heat involved, increases both the amount of juice extracted and the amount of nutrients retained, and also produces a thicker juice with more fibre retained. The smaller footprint of a slow juicer means less space swallowed up on your worktop; conversely whole fruits often need to be chopped into smaller pieces before they can be placed in the machine. No blades and no high-speed operation means a quieter machine, and of course there are no sharp blades to clean up afterwards.
Unlike their 'slow' counterparts, fast juicers use centrifugal force to shred the fruit and veg before spinning them at high speed to separate the juice from the pulp. They often feature large food chutes and can get through a greater amount of fruit in a short space of time, without it needing to be chopped up first.
There is a school of thought that this faster, less gentle process increases the heat of the fruit, which can potentially destroy valuable nutrients, but this is not generally considered enough to make a significant difference to the final results. Producing a thinner juice with less pulp, a fast juicer is perfect for those who like smooth juice, however unlike most slow juicers, fast models cannot usually juice wheatgrass. Fast juicers are ideal for preparing several portions of juice in a very short space of time, but are a little noisier in use.