If you only had to have one I bet most of the members here with more experience then I have would recommend a Norton 4/8 combo. If you wanted a Belgian Coticule then a natural with the blue being approximately a 4 and the yellow an 8. The natural would be quite a bit more expensive. I really like the Norton 4/8 and from what I have read it is thought by most to be an ideal stone to learn on.