Combi stones have a lot of drawbacks. Among them: It's very unlikely the sides will wear evenly; which means that when you've gone too deeply into one side, you'll have to throw away the stone. They tend to run fragile in two senses -- they sometimes come apart at the join (glued together), and if one side breaks or the corner crumbles or whatever, the whole stone is wrecked. You end up doing FREQUENT flattening; because there's no "other side," you can't put it off. Whichever side you think is really great, the maker chose the other for its own reasons and not yours. Also, few manufacturers use their "top of the line" stones for either surface. Last, when it comes to those few, good combis, you just don't save enough to make the compromises worthwhile -- at least not in my opinion.
The best two stone set blanket recommendation I can think of is Bester 1200 + Suehiro Rika. The pair will run you around $80. Neither stone is without issues. The Bester is very hard and requires long soaking before use. The Rika dishes easily, and breaking the mud down fine enough to polish at the stone's nominal 5K# requires some learning. But still... They're excellent, long-lasting stones which are simultaneously easy to use and good enough for "experts." The Bester in particular is very fast, can handle a lot of scuff from even the coarsest stone, and leaves a surprising amount of polish. The Rika finish -- which can seem like anything between 3K and 5K depending on how you use the stone -- is excellent for kitchen knives. Additionally, the stone feels great and gives a lot of feedback.
No matter how much you spend, you won't beat them for speed or edge quality by much.
But, one size doesn't necessarily fit all. Whether those are the very best stones for you or your knife kit, I can't say.
FWIW, I own and use a Bester 1200, but not a Rika. My intermediate water stone is a Chosera 3K, which itself is a very good stone but too expensive for what it does. If I were putting together a new water stone kit from scratch, I'd probably replace both the Bester and Chosera with a Gesshin 2K, which is as fast as an aggressive 1K, but polishes as well as the Chosera 3K -- fine for most kitchen knives. The Gesshin 2K runs $95.
I'm very impressed with all of the Gesshins I've tried. Up to now, I've always used four-stone kits (one to profile, two to sharpen, one to polish), but if I were putting together a "cost is no object, ultimate" sharpening kit from scratch, I'd get the Gesshin 400, the Gesshin 2000, and either the Gesshin 6000 or 8000. Perhaps I should add that since I already have a Gesshin 8K, the 6K is only "presented for your consideration." Bottom line: Gesshins are very expensive, but unlike Choseras, they're enough better than the "common clay" to be worth it. Of course, opinions differ and some people swear by Choseras as "the best." I don't argue with that so much as see things a little differently.
Some Inside Baseball: The Gesshin 4K and 5K are very different from one another, and although the grit levels are very similar they assume completely different roles. The 5K is a good final stone, while the 4K is more of an intermediate step to a high polish. But since the 8K -- which is as high as I'd ever want to take a kitchen knife -- reaches the 2K without any problem, neither the 4K or 5K make any sense at least not within the context of my kit. While that may not apply to what you want to do it all, the relevance is the realization that putting the right stones in your kit pays off.
FWIW, the quality differences in Japanese style synthetic water stones are strongly related to the type of binder, the relative hardness/softness of the stone, the type of abrasive, and the relative concentration of abrasive in the binder.
Whatever stones you buy, don't forget to soak the stone well, flatten the top and bottom, and relieve all of the edges and corners before using.
Edited by boar_d_laze - 5/30/12 at 9:05am