Diamond sharpeners can be quite aggresive and generally produce a rough finish. I prefer a 3 stone set of Spyderco's 302 ceramic benchstones.
I'm a total rookie at knife sharpening, and after much research, product comparisons, and soul searching I ordered an Edge Pro Apex. It should be here this week, so if you'd like I can give you a newb's perspective on using it...
the best thing to is to learn to sharpen by hand