I have 3 that are tied.
1. I had an old Arabian gelding named C.J. He was 24/25 when we got him and I took lessons on him for a summer with my mom who was recently getting back into riding. C.J. was my first horse (before I'd owned a pony). The pony was a stubborn little piece of work but C.J. was 100% perfectly trained - pivot, sidepass, flying lead changes...he had all the buttons, I guess the lady who had him before us competed on the national level or something with him. Anyway, he was such a good guy. He was the first time I cantered. I was over the moon haha.
2. Same horse, C.J. and I were on the trails on a group ride and we were all loping along on a wide stretch of path and some idiot kid comes out of no where with a dirt bike right in front of us and C.J. swerved to the side, I lost my balance and he moved back and tried to catch me and finally just stopped and I fell forward on his neck and landed on my back in front of him. He had been shuffling his feet when I fell and I looked up and just saw his on hoof right above my head and then I saw his nose poke over his knee and he moved his hoof to the other side of my head and just looked at me and waited for me to get up.
3. My current horse, Sonny, when I test road him on the trails the day I brought him him home. His old owner (my mom's friend) new speed was important to me, so she got on her her horse and we raced - just the two of us. Both horses are barrel horses that she'd trained herself from the time she bought them. She bought both when they were 2 and I got sonny when he was 15. I love to go fast and it was just fantastic.