*What are the most prestigious/most competitive ultramarathons in the world to win?
*What is your favorite ultra? What is the most beautiful ultra? Is there a bucket list of ultras that most amateurs should aspire to run?
*Who is the GOAT of ultra running?
*What are the hardest course/world records to break in ultra running?
Here is my background in order to evaluate my responses to the questions:
I completed over 100 ultras during the 1978 - 2015 timeframe. My PRs at standard ultra distances are 50K - 3:07, 50 miles - 5:35, 100K - 7:31 and 100 miles - 18:49. Twice I was on the U.S. national ultra team.
I don't feel competent to judge what is today the most prestigious/most competitive ultra to win. Back in the 1970s and 1980s, the most prestigious/most competitive ultra was London to Brighton. That race was, at the time, considered an unofficial world championship. Now there is the world 100K championship. There is also a 24 hour world championship. Some will insist that Western States is most important. Others, Comrades. I have run London to Brighton, the world 100K championship, Western States and Comrades. If I could have won any of the four, I would take Western States but only because that race is the most important in the U.S.
In my opinion, by far the best ultra (even if it is not the most prestigious to win) is Comrades. (I ran Comrades in 1996, shortly after apartheid ended, so Americans could finally run without adverse repercussions.) Comrades is to South Africa what the Superbowl is to the U.S. The entire country shuts down for the day to follow the race. There is nothing comparable in U.S. running. In 1996, Nelson Mandela, then president of South Africa, handed out the awards. Comrades was my best ever running experience in 50 years of competitive running.
Picking the male GOAT of ultra running would be as difficult as picking the greatest male runner of all time. How do you compare Bolt v. Bekele? The same problem exists in ultrarunning. How do you compare Don Ritchie v. Yannis Kouros?
The female GOAT of ultrarunning is Ann Trason. She set records at both the short and long ends of ultrarunning, dominated Western States for years and won Comrades. Most importantly, she was probably the only female ultrarunner which the top male ultrarunners feared. (Full disclosure - I have known Ann for decades.)
Those are my thoughts and I am sticking with them.