What is the fastest horse in red dead redemption

That all depends on you. If you don't want to get a horse outside of missions, then your best bet is the Kentucky Saddler, which you "get" during the mission Wild Horses, Tamed Passions. However, the fastest horse in the game is the American Standardbred, although it is weak in stamina and health in comparison. You must, however, break this horse before you can get it. It can be found in the areas of Tall Trees and Beecher's Hope, although I found it once near Thieve's Landing. Also, if you got the pack, the War Horse is the best horse you can get.