The best knife sharpener is the one that is functionally flexible as well as durable for the price that you have paid for it. There is no single unit that is the best for all. It all depends on one’s requirements and budget. We strongly advise you to go through our write ups of different knife sharpeners so as to compare and choose the best one for your knives.
The Whetstone 2-Sided Sharpening Stone is made from professional grade corundum and will sharpen everything from a razor blade to a cleaver and even a machete, should you happen to have a machete lying about that needs sharpening. This is the simplest type of sharpener it’s true but the company have obviously put a great deal of thought into the product.
Our second entry from Chef’s Choice is the 463 Pronto Santoku. This manual sharpener is super-simple to use and delivers fast, high quality results every time. While this is a “2-stage” system there’s nothing complicated about it. One slot is for sharpening and the other for honing. Both stages utilize diamond abrasive surfaces so your blades will retain its edge for a good long time. 

Suitability - Your desired knife sharpener must be suitable enough for the job in hand. For longer blades, you will need a correspondingly large knife sharpener, and for very sharp blades, a hard abrasive material such as sharpener will be needed. Quite frankly, the sharpening material of the knife sharpener should always be harder than the blades of your knife.