The 240 thing is a no-brainer for me. But I have thought about it some more. And I honestly don't know what stone I would recommend to a newbie. I did not own a 1k stone until many years after I bought my first water stone and after I bought it I mostly only used it to have a third stone in the rotation for three stone method stone leveling. After a few years of using the two stone method I leaned why that is not a thing people recommend. That tends to amplify the dishing in one stone and convex the other.
In my case, I had a dished Shapton Glass 500 and a convex Naniwa Super Stone 2k. Adding in a Shapton Pro 1k and adopting the three stone method helped a lot. This was still long before I learned about Atomas. And I have still never actually bought a 140 for some reason. So I guess my answer is that it would be really hard for me to recommend just one stone. And if I did I would lean toward a diamond combo over synthetic water stones.
Nowadays here's what I use for 99% of my sharpening.
Naniwa Diamond 600 if any kind of bevel reset needs done.
And then finish or touch up according to what kind of edge I want. I rotate through different naturals but here are the options currently in the drawer.
Coarse washita - 1k
Fine washita - 2k
Coticule - 4k
Llyn Idwal - 6k
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