Letsrun, thanks for hosting this discussion of ultras. I have participated in a number of ultras, and I confess to wasting too much time reading about record-setting performances, but really I think the discussion misses the mark about what ultras are really about, at least to me. I run because its fun and I enjoy it, and I participate in ultras because I consider them to be an adventure. I would wager most ultra runners don't care that much about records, because they are more interested in having a good time, and they realize that most of these events are not really competitive events. Yes, they are races, and yes, there are competitions, but for almost everyone that is not the first or second or even the third most important thing. Even the famous ultra runners like Jim Walmsley and Sage Canaday can't be making all that much money, and outstanding runners like Mike Wardian still work full time jobs.
Anyways, I would love for you to include some discussion about who are the best race directors and who are the people who have done the most to promote ultra running. For example, Gary Cantrell, and his ridiculous races have gotten a lot of people interested in ultras, and events like the Barkley marathon and Big's Backyard Ultra seem pretty incredible, although there are not any course records that could really be considered the "best."
1) Best course records (Comrades, Western States, UTMB, etc).
The fastest known time on the Appalachian Trail. The reason this became the best course record is really thanks to the great David Horton who first ran the trail in 1991 in 52 days, and the current record by Karel Sabbe stands at an outstanding 41d 7h 39m. Scott Jurek and Karl Meltzer have both previously held the record before. https://fastestknowntime.com/route/appalachian-trail
It is sad that running doesn't have something similar to the Tour De France , or in my mind, the much better Race Across America, or even better Trans Am Bike Race. Although Pete Kostelnick has shown that you can put in a good showing running across the country, and his 42 days from San Francisco to New York should be in contention for the best record.
2) Best records at runs less than 24 hours hours (50 miles, 100k, 100 miles, Grand Canyon Rim to Rim, etc).
I think Jim Walmsley's R2R2R on the Grand Canyon is the best short course record as it is an outstanding time in what may be the most stunningly beautiful place in the world.
3) Best 24 hour and longer races (24 hours, 48 hours, 6 days, also includes runs across US, Britain, Sri Chinmoy 3100, etc).
I think the 6 day records are really the best, especially because of the long history. I love the fact that back in the 1870s, at least according to Wikipedia, a rich dude was funding a series of races to determine the "Long distance Champion of The World". 500 miles in 6 days was incredible, and Yiannis Kouros and his current standard of over 1000 km is just mind-blogging.