First, I live in Sacramento, close to the finish of the WS100 and first ran it in 1978; I am a 3X finisher there. I have also run Comrades....and London to Brighton on the WORLD stage. Of course I have also run many of the 50k to 50 mile distance events in the general Northern California area, e.g. American River 50, Jed Smith 50, etc.
For me, no doubt the most impressive/outstanding ultra is....Comrades with over 11,000 starters and almost that many finishers. The history, challenge to run fast and not just finish, and the NATIONAL ATTENTION that event gets in South Africa make events like the WS100....small cult experiences.
As an example of a difference between Comrades and US/California/Sacramento attention to the "ultra scene," in the recent Hoka One One 100k/50 mile record challenge here in Sacramento which was an amazingly well-staged event by the way. I did my own morning training session near the finish area and then did a "cool down" going backwards on the final look section of that course. Our local newspaper DID NOT COVER IT WITH EVEN ONE(1) COLUMN INCH !!!!!! It did not get major local TV coverage here.
Comrades, on the other hand, once tried to reduce the NATIONAL LIVE TV COVERAGE from 12 hours to 11 hours, and there was a MAJOR PUBLIC NATIONAL OUTCRY!!!! I have been out for lunch in Durban the day before Comrades and the waiter asked, "What brings you to South Africa?" When my wife and i replied that we were here to run Comrades, he KNEW THE SPLITS/KM to hit the various cutoffs for the 85-90km distance of that event (varies by starting/finish direction). Try that TEST OF PUBLIC INTEREST ANYWHERE ELSE IN THE WORLD for a nearby ultra !!!!!
In South Africa, you virtually do not dare wearing a "runner's shirt/shirt from a running event" if you have not run Comrades, as you WILL BE ASKED...."How many times have you run Comrades?" Not "whether," but "how many?"
I'm sorry to disabuse those of my local friends of their WS100 passions; they can rightly worship at whatever alter they choose. I count Norm Klein as a good friend; Greg Soderlund really learned his race directing from working with me; he rented a room from me during our mutual "single days." Greg met his wife through me. Yes I have GREAT respect for the WS100, as I did for London to Brighton (before it...got cancelled). But Comrades is on a totally different and higher level in so many ways.
Oh, and I wrote the chapter on "training for Ultra Marathons in one of the Runner's World general training books (edited by Hal Higdon), and my chapter was reprinted as a training guide for Comrades at least once. I have run under 7 hours on the American River 50 Miler and under 6 hours for 50 miles on a straight road course (Jed Smith) and twice broken 24 hours at the WS100.