Yes, i know it a very open and near impossible question to ask, because of all the different types of race/horses, but it would still be good to hear peoples thoughts.
Possible Contenders: (Any Others i've forgotten?)

Phar Lap
Kingston Town
Tulloch
Manikato
Bernberough
Ajax
Sunline
Super Impose
Better Lossen Up
Carbine
Gunsynd
Octagonal
Flight
Archer
Makybe Diva
Lonhro

What do you guys think?