Yes, I love the bigger horses as well. I kept that HUGE black Shire horse Arthur gets at the beginning of the story mode all through the single player campaign because I loved it from the moment I saw it, especially when Hosea described it as "mean" or something, lol. MY KIND OF HORSE. I also loved how tiny every single other horse looked compared to it, lol.
As for the multiplayer... my only wish is that the Level 20 Trader Kladruber came in black (I wish we could pick not just gender but also choose between the most common horse coats or something, I mean we have a zillion colors to pick from when it comes to cars in GTA as well, so why not here) but hey, I'll take the gray one, too. All good.