Another vote for Work Sharp Ken Onion Electric Knife and Tool Sharpener. It keeps all of my knives screaming sharp.
I use 12" diamond rods on my knives, but I learned so sharpen free hand on stones about 50+ years ago. The diamond rods are excellent.
But my amigos can't sharpen to their own satisfaction. After reading some glowing reviews on this machine here a couple (or more) years back, I suggested it to a friend of mine that has bought different systems and had no success. He loves it.
He has learned how to repair the damaged edges on some of his knives, and has turned into a sharpening monster. Nothing is safe, and he told me he is now sharpening knives that have been unused for years as the steel was too hard to sharpen with his poor skills.
I do enough sharpening for others that I pick up enough for a new knife every once in a while, but I am tired of damaged knives and chewed up edges and the time to work them out. And I am getting more knives to sharpen on a regular basis. So I bought the KO edition of the Worksharp (wider belts, an additional guide, more angle choices then the base model) and I love it. This machine is about as bullet proof as you can get if you follow the instructions. I had the movement and stroke speed down on one knife. You could probably burn the blade if you went to sleep when using it, or made it a point to try to, but if you follow the instructions you can get an amazing edge even on crappy knives.
I had seen these on sale at different gun shows and walked right by them for years. I admired the edges the guy that sold them got, and he had quite a schtick going. He would sharpen a single blade on a knife for $5. If it was a larger hunting knife that just needed a touch up, it was $7. He sharpened your knife and then sliced ribbons off a piece of phone book pages. If you bought a Worksharp from him at the show, he waived the sharpening cost. I don't use it to touch up my own knives, but for resetting and edge, rebeveling, repairing damage, or sharpening my restaurant buddy's knives, this thing is the stuff.
Robert