Definitely Adult Epona. She's faster than her younger version and the King of Red Lions. And I like her saddle too. And I always had fun making Epona jump over fences and stuff. And in OoT, you had a bigger space to ride her in and more places to make her jump. And you can play a number of games with her too, such as the archery game in Gerudo's Fortress and Malon's obstacle course in Lon Lon Ranch. There wasn't any game you could do with Epona in MM (I don't consider Romani's balloon practice a game) and there was only one game you can do with King in TWW.
So yeah, my vote goes to Adult Epona. I favor her by far.
