2 very different stones. I wouldn't look too much into grits difference between those 2. People like Naniwa for their feedbacks, consistency and auditory. Same goes for Shapton. It's more of a preference thing. Both are good, I like Shapton because it's resonates with me. That doesn't mean Suehiro, Naniwa or any other brands are bad. For example, people loves Suehiro Rika, (the 5k but is actually 3k in grit and polished like 5k, unique stone) buttery, pleasant feedback. Ouka 3k, popular stopping grit, I have read many actually like this stone. Suehiro 320, love and hate, soft, and fast from what I have read. Suehiro Cerax 1k seems to hold its own, it's still a popular stone, feedbacks, and speed. I have it but haven't used it. I should soon just for the heck of it. All in all, any of those will do you solid. Phew, I rambled on again
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Suehiro Cerax 1k/Ouka 3k or Rika 5k all are soakers.
Shapton Glass 500 or PRO 1k-1.5k/SG2k or PRO 2k all are splash and go.
Naniwa 800/3000 all are splash and go.
In due time, Atoma #140.
When it's time to thin and reset bevels, Shapton 500 usually do the job, but if severely thinning, then Shapton Glass 220 or 320. Same applies with PRO 220/320. Atoma #140 a must to keep the surface flat.
Usually you'd want to condition stones with Atoma #140 to rid off some "coating" on the stones to reach the full potential of sharpening experience.