A "good" sharpener will be different from person to person. But I sincerely doubt you'll find "good" stones unless you've completely mastered freehanding. However each system have their own learning curves, with some being steeper than others.
For freehand, I think it's a safe bet that DMT diasharp stones sit near the top(if not directly at the top). Compared to japanese waterstones, they're low maintenance(water is not "required", no need to flatten, no need to soak), and they cut faster and work exceptionally well on modern wear resistant steels.
For a guided system, Edge Pro and Wicked Edge are duking it out for supremacy. On a personal note, I haven't touched my Edge Pro in over a year because of the time it takes to get a single knife from dull to push cutting paper sharpness, as well as the numerous and tedious tasks required to make sure the angles are accurate(trust me, marking the edge with a sharpie and changing the tape on the table between every stone gets pretty tedious). Also, I feel the Wicked Edge has more potential as I would expect diamond stones to cut faster and hasten the process, as well as not having the need to flatten the stones. I also always felt that a system like the Edge Pro would be more effective with a clamp system to hold the blade in place.
For power tools, there's the Paper Wheels which is like grinding wheels on steroids. The abrasives are better cooled than typical grinding wheels, making it safer to use on knives without the risk of ruining the heat treat(still need to exercise some care though). But as with power tools, the slightest mistake will be amplified about a hundred times. Since it's essentially a form of freehand, my edges sometimes look like someone tried to grind 3 different angles on them. The flipside is that what would have taken me 30 minutes to go from dull to push cutting paper would only take about 5 minutes with the Paper Wheels. At $50 for the wheels, and another $50 for the bench grinder, a total cost of $100 makes this relatively cheap($200 for an Edge Pro, $200 for a Wicked Edge, $200 for a full set of DMT benchstones without the XXC and EEF stones)
I believe belt sanders are the old favorite, particularly with factory grinds IIRC. They're relatively low cost in terms of the machine itself as well as replacement belts. That said, I believe the Work Sharp Knife & Tool Sharpener deserves particular mention for being essentially a portable belt sander with limited angle guides(20 and 25 degrees per side). There can be nothing more simple than sticking your knife in the guide and sliding it through, combining a consistent angle with fast sharpening. For those willing to do a little legwork, you can have more belt options than what comes with the sharpener. The Micro-Mesh MX belts in particular are specifically for metal work. It's also easy to get convex edges with the system, which I believe is historically proven to be a very durable edge if japanese katanas are any example. At $69.95 and $0.52 per Micro-Mesh MX belt I find this system to be a very good bang for your buck, as well as your time. I have recently put an order in for one, but the high demand drained the supply and I'll likely have to wait another 2 weeks before I can use it myself.
In the end, what it all boils down to is:
-How much are you willing to spend?
-How much time are you willing to take when sharpening?
-How much practice are you willing to invest?
Look no further. No I don't work for the Wicked Edge and Clay Alison is not a member of my family! I just a happy old guy who finally found a sharpening system that doesn't suck. Pricey, perhaps but worth every penny. False economy is buying cheap stuff over and over again. I am just a happy customer and I don't mind saying so.