I personally like the DC3 or DC4 stones - the diamond side is very good and quick for reshaping a blade that has been a bit chipped, while the ceramic side gives it a good honed edge.
They are a bit small, so I have started to use them a bit like a file - rather than placing the stone on the ground and moving the knife along the stone, I now hold the knife still in one hand and rub the stone in circular motion along the ede of the blade to sharpen it. Difficult to explain in words, probably better if I were to post a picture.
Only thing is that the stone is going to cost more than the knife (assuming that you are getting one of the £10 moras). But I think it's worth the money. I've found it much better than my old chisel sharpening stone.
Geoff