In my opinion, it is necessary to separate the tracks in "indoor" and the tracks in "outside" because it is not comparable :)
For the indoor I would say Le Grand Palais in Paris, Le Palexpo in Geneva, London Olympya in London.
For the outdoors, the Vichy terrain, all the tracks where events such as Wellington are held, I have a huge favorite for a stable In the USA this is the place where the World Equestrian Games will take place !! This is the Tryon International Equestrian Center in the town of Tryon in Northern California.
Have a good day :)