Horses have unique abilities
So, those unique traits horses possess are four-fold: strength, speed, stamina, and temperament. Each of these are self-explanatory, aside from maybe temperament which gives an indication of the horse’s docile-ness. Arguably, with the most common mode of traversal throughout Hyrule being horseback, Link needs to acquire horses with the most stamina. Of course, the wild steeds throughout Hyrule all have individual style – picking the one that visually appeals is equally valid as a stats-focused approach.