Too follow up from Millions, SRS-15 and SG-2 are considered fully stainless, and ZDP-189 also I think, HAP40 being semi-stainless.
I've heard, just about invariably, that ZDP-189 is prone to chipping, and everyone says a bitch to sharpen. I'd say the other 3 comprise the best-list here inclusively.
SRS-15 at this time has just one maker, I believe, whose knives are branded under names like Akifusa, Ikea, Artisan, Geshin Kagero, and whoever else. I can't say enough good about this stuff in terms of edge holding, and it takes an edge about as good as any non-PM stainless. I have found it relatively tough also, especially considering it's around 65RC. I don't find it chippy at all.
There are a few makers who do SG-2/R2 very well. It is probably winner of keenest edge among the PM steels, I've heard it compared to the best of white steel, it's likely close anyway.
HAP40 is wonderful stuff by all accounts also, and it along with SRS-15 I believe have the best edge holding, but I think SRS-15 may have it beat there.
You have a downside with SRS-15 as there is no variety there. Everyone is selling the same knives, so you either like those geometries and such or you look to another supersteel. Not that much better there with HAP40. And all the decent knives in R2 seem to be lasers, though I don't know all that is available.
There's some really stupendous high-wear stuff like S110-V, it has superfine carbides but poor edge stability, can't handle a very acute edge. It may actually have a replacement already.
I'm confident there will be even better coming down the road in the not too distant future.
If I were looking for a new knife, at this very moment, it would be one in R2. But I wouldn't be unhappy at all with AEB-L/13C26, Ginsan/19C27, 14C28N or AUS-10, and maybe some others, from any maker with a decent rep and geometry close to my preferences.
So pinning down the best presents I think some insurmountable difficulties, but a range of the best not so much so.
Hope all these replies so far help.