In terms of man-made waterstones, I have a set of Shapton Professionals: 1000, 5000, and 8000 grit, and am really happy with them. If I had to do this over, I think I would get the 15000 grit waterstone instead of the 8000 grit. At the time I bought these waterstones, the 15000 grit was considerably more expensive than the 8000 grit, but for whatever reason, they seem to be priced identically now.
I haven’t done a detailed head to head comparison of different brands of waterstones, and I don’t think I ever will. I have quickly tried different waterstones here and there, and I’m fairly confident in saying that any of the Japanese brands that are readily available in the U.S. will work well: King, Bester, Sigma, Ohishi, Naniwa, and any others I might have forgotten to mention.