Ah, sharpening stones. Such a contentious subject, despite the fact that the metal doesn't really give a crap what's used to sharpen it. All you really need is an abrasive harder than the steel itself and a flat substrate. That could be anything from a fancy diamond plate to a Japanese waterstone to sandpaper stuck to glass to a cinderblock, all will work just fine. Oh, and I'm not kidding about the cinderbloc
That said, there are some that work better than others for certain applications. For knives, i like a long, narrow (in relation to length at any rate) continuous diamond stone. The length let's me work on longer blades easier, it being narrow seems to help cancel out any warp in the plate, and diamond cuts aggressively, even in some of the fancy wear resistant steels like D2. The one I use most is a double sided stone, bout 2x6, maybe a little narrower, and has what I believe is about 400 grit on one side with the other being in the 800-1000 range. I think. Dunno for certain. At any rate, it puts an excellent edge on a knife and cost me a whopping $6.
My chisels, funnily enough, never touch that plate. A chisel works better with a much more polished edge than a knife does, and to get the best edge the sharpening surface needs to be dead flat. The easiest way for me to do that is to use some spray adhesive to stick sheets of wet/dry sandpaper to a piece of granite. Dead flat surface, and I can do from 220 all the way up to 2500 grit when sharpening my chisels. It's also dirt cheap, which is a big plus.
As far as stone recommendations go, I'd go for a continuous double sided DMT stone in your case, in the coarse/fine grade. Diamond is a pleasure to sharpen with, it never really looses its aggressiveness, and DMT is m own for making a quality product. I like the continuous stones over the little circle pattern ones because the continuous stones can be used to sharpen small points, like a parting tool. The dot type plates have a bit of an issue with the same task.
I'm not a big fan of Arkansas stones, and have no patience for Japanese waterstones. The Arkansas stones are okay, I guess, but don't seem to cut very aggressively and have a hard time on stainless or wear-resistant tool steels. They also tend to clog easy, so you can't use them dry if needed, and are a royal b**** to flatten, which you'll need to do every so often. I still use an Arkansas stone from time to time, but it's not my favorite. Japanese waterstones are great, if you have the time to soak them before every use, dry them off when you're done and flatten them every 30 seconds. Personally, I don't have that kind of patience, if I needed the superfine edge one of those waterstones could give, I'd just as soon slap a piece of sandpaper on a piece of granite and be done with it