david weaver
I also have a bunch of sigma power stones (fewer than I used to have). I don't find any favor for the SP 13k over the shapton stones, and the middle stone can be anything from any maker, as it's not really necessary for anything other than cosmetic knife polishing.

The SP 13K is simply too soft, and it's slower than the Kuro 12k because it's finer. But the fineness is not functionally useful - only the kind of thing you'd notice if you're trying to take wide 2 thousandth pared shavings off of maple (even then, it's transient). More clearly, I believe the 12k kuro (without looking it up) is slightly north of 1 micron in particle size, the sp 13k is something like 0.73.

The SP 13k also absorbs water, which is a real pain if you're using a dry stone and you want it to be a wet one without having to keep spraying it. Not a big deal if you're in the shop all day, but the day you're in for two hours and sharpen one thing or two, it's kind of a pain.

There is a slightly higher learning curve with the kuromakus, but it'll be worth the trouble to get through it.

For a little while in the mid 2000s (to late 2000s?) there was a thing going where every subsequent stone introduced was supposed to be better.

King, to shapton, to naniwa superstones, to chosera to sigma power. All of them work fine (I'd prefer to avoid the softness of the first and third mentioned, and chosera are not low-maintenance stones, and for the price...I just don't know what you really get). I don't think anyone has improved on the shaptons, and that includes shapton themselves (when they started introducing glasstones, then two types of glasstones).

All of these have some sort of alumina in them, and the binder differs a little. I developed a preference as follows after trying way too many stones:
* shapton 1k pro or bester 1200
* chosera 3k or shapton 5k (the 5k gets some bad press, but you have to learn what it does and what it likes - the chosera is expensive, but good)
* the shapton 12k or 15k.

Various stones have different feels, but economy of use is hard to beat in the first and third bullet point (I rarely used the middle). Keeping the shaptons neatly dressed and with a bit of wet slurry on them makes them much easier to use. They should last several decades - at least.