Before deciding on a best / most competitive ultra or GOAT, it would be helpful to break down ultras into categories. Then we could decide the best ultra(s) and GOAT in each category. After doing that, we could see if any one course is the best overall, and whether there is an overall GOAT overall. As a start (adjust these as needed):
Road Ultras (50km - 100km)
- Roughly speaking an extension of road marathons (but typically hillier).
- Runners excelling here typically have a road or track background.
Most Competitive/Prestigious:
- Comrades
- Two Oceans
- IAU 100k World Championship
- GOAT: ?
Trail Ultras (50km - 100km)
- Substantially more vertical change than a road marathon, but runnable (see Mountain Ultras below for non-runnable courses).
- Typically a fast marathoner is likely to be a fast trail 50km - 100km runner (aside from extreme/outlier courses), with proper adaptation to vertical change
Most Competitive/Prestigious
- North Face 50
- ???
- GOAT: ?
Trail Ultras (100 mile)
- Separate from 50km-100km, reasons:
1. Historically, fast runners in marathons, road ultras, and 50km-100km are typically competitive, but not automatically near the top when moving to 100 miles.
2. More per-race variance due to fueling, course conditions, and race duration, as compared to 50km-100km.
3. There are a substantial number of 100 mile races;
Most Competitive/Prestigious
- Western States
- UTMB (which is interesting competitively since it almost crosses over into a mountain ultra)
- GOAT: ?
Mountain Ultras / Sky Running
- Characterized by extreme ascents and descents, often requiring scrambling and hiking.
- A very fast and competitive sky runner may be slow (relatively speaking) on a flat marathon course.
- A very fast road marathoner is typically competitive, but the terrain and race is so vastly different than a flat road marathon that they are not automatically near the top.
Most Competitive/Prestigious
- Zegama
- ???
- GOAT: Killian Jornet
"Extreme" Races (this could be broken down further)
- The race format itself is extreme, due to time, distance, or unique characteristics.
- 24 hour record (on a track)
- Barkley
- Tour de Geants
- GOAT: ???