I've got a lot of sharpening equipment but for just knives I like the Spyerco Triangle Sharpmaker mentioned above or the Worksharp Knife and Tool Sharpener.

Water stones, oil stones, ceramic stones, and diamond stones work well but it takes more skill to stay on the bevel of a two bevel knife. I do use stones on single bevel knifes. They have larger bevels and the stones handle the flat side bur easily.

P.S. Any of the above systems will sharpen a knife. Get a good one and learn to use it. Take it from me, you can
spend a small fortune trying to find the "best." The key is experience with one system.