I normally sharpen "freehand" with a flat carborundum or diamond stone.
But I received one of these "Speedy Sharp" knife sharpeners for my birthday, and have been pleasantly surprised by it. It's small enough to carry in your pocket, and touches up a blade in a few strokes.
Normally, I have a strong aversion to carbide pull-through sharpeners. They remove too much steel, they leave a jagged burr edge, and they are never at the right angle for the knife in question.
But this little dude, which boasts "MICRO 100 Super Carbide" and a lifetime warranty, works much better. It takes off a minute amount of steel and you adjust the angle, freehand, based on the blade.
It particularly shines with lower-end steels, which my 'beater' blades typically use. The 420 knife and carbon machete steels get a sharper edge than you may have thought possible.
I don't think the edge would last as long as a stone-ground edge. But for hard-used knives, you can touch up the edge with just a few strokes.
It seems like just about anybody can put on a decent working edge with this gizmo. I can't say that about flat stones.
I bought a few extras on sale (about $8) and gave some away at Christmas.
Here's the link:
http://www.speedysharp.net/Usual disclaimer: I have no affiliation with this company, etc.