I'm going to cast another vote for Kouros's 24-hour record. It's just ridiculously good. Who is the 2nd-best 24-hr runner of all time? I don't think anybody else has gotten in the 180's.
I like to think of it in terms of kilometers, because he broke through the 300k barrier. I've run quite a few ultras over the years, so I have a fair sense of what a good time is. For 50k, breaking 4 hours (on a fairly easy course) is solid. It's fairly close to a 3:00 marathon - maybe not quite that level, but close. So anybody who can break 8:00 for 100k is a VERY solid performer. Doing three sub-8 100k's back to back to back is just about unfathomable.
Camille Herron's 162.9 miles was pretty spectacular, but she's not within the 10-12% that most women's records are in comparison to men's, so I'd say Kouros's mark is intrinsically superior. Perhaps she can improve, though.
The best women's mark (and by quite a ways) has to be Tomoe Abe's 6:33 for 100k. But it was so out of the blue, with no other ultras to her name that I know of, that it just seems odd. She was a fast marathoner who I believe won WC bronze, so I think it gives a hint of what elite marathoners could do for 100k if they pursued it. Especially those unbreakable Japanese.
My 2nd-place vote would go to Kouros's 6-day record of almost 1039km (644 miles or so). For me, I would consider that a solid 3 months of training mileage.