I've used a ton of different stones, from DMT, swix, holmenkol...so far my favorite has got to be the diaface moonflex stone. I've only got one, it's a mid-grit (400 maybe?) and it works great. just toss a little water on it, use it and put it away. I just learned a good way to clean it the other way cause mine is a little dirty. From experience, I would stay away from holmenkol stones. it's just a piece of metal with a diamond stone...sticker...if you will. After just under a season's use it's started to slip off the metal. that plus they get really dirty really quick and i haven't found an effective way to clean them.
swix also has a good set of stones as well, i have a really high grit (600 or 900 maybe, i don't remember
) that I use as a finishing stone that works great as well