Diamonds are locked in place (embedded in a single layer into a metal plate), so they leave a very even scratch pattern. They are also the hardest material known to man, so they cut very fast. They are excellent for the highest-wearing steels (D2, etc.). They can leave a very nice edge and tend to be coarser than the advertised grit, based on my own experience. They can be overkill for softer steels and can be very hard to deburr if you're doing everything on the stones because they cut so fast and coarse. As a result, they really benefit from stropping afterward with a loaded strop. They work best after breaking in (a few dozen sharpenings or whatever) and smooth out. They will eventually smooth out to the point they need replacing, but it will take years, maybe 10 years of constant use (we're talking high quality manufactured stones like Aotoma and DMT).
Water stones are my favorites. I don't use Choseras. In fact, the only water stones I have are Nubatama Ume, Naniwa, and Arashiyama. I mainly use my Omura 150 grit and Arashiyama 1k and 6k. Water stones, even relatively slow-dishing ones like the Arashiyamas, are much softer than ceramic. You can easily gouge a water stone with a knife. They work well on almost all steels except the very high-wearing "super" stainless steels, but they still work, just a bit slower (I regularly sharpen S30V, VG10 and other high-wearing steels with my water stones). The abrasive releases from the binder and creates a slurry or mud, which both sharpens and polishes above and below the apex. They can produce edges finer than their advertised grit from breakdown of the slurry. A hard stone like a Chosera probably cuts fast and leaves a nice, smooth edge.
Ceramics are very hard, load quickly, and cut pretty fast. They can be used dry or "splash and go" style. They tend to burnish/polish edges especially at higher grits like the Spyderco UF and put a mirror polish on a bevel. They can put a very fine edge on a knife. I don't use my ceramic stones very much these days because I don't like the way they load up and slow down so quickly.
I think water stones are the most versatile stones, and I think they are great for general sharpening of common steels at any grit. I like my Arashiyamas, but I haven't tried a lot of water stones. I'd love to get the full Nubatama Bamboo range and the full Chosera range. I would also like to try the "green brick of joy" 2k and the "snow white" 8k stones (both Naniwa stones). But if I bought every stone I wanted to try, I'd be in debt. I've already spent over $1k on sharpening stuff, probably closer to $2k.
So I think I'm going to just try to be happy with what I've got, which is already a lot.
If you want to get into water stones, you could start with a King 1k and 6k. They are cheap, widely available, and are good enough for Murray Carter. I've heard they are soft, slow stones and good general-purpose stones.
