Join Date: Apr 2010
Location: Near Boston, Massachusetts
I agree with epicfail: diamond plates are almost definitely the best value for the money. I've been using the DMT Duosharp stones for a few years, and I have yet to find something I don't like about them. I find that with coarse, fine, and extra-fine surfaces, the limitation is my skill rather than the tools. I also have a strop with a very fine compound on it that I use as a touch up during work. So I'd probably go for two Duosharp plates, the extra-coarse/coarse and the fine/extra-fine.
I do regret having bought the 6" plates, though: they're too narrow for me to use for the iron of my jointer plane. Go for the 8" plates, and you'll be a lot happier.