I really like the helper animals from the Oracle games. They were all very unique, never before seen in the series(unless you count Dimitri, because I think he's a dodongo of some sort), and played a good part in the game. They kind of mixed things up a bit and were different from what we're used to. I loved how they were used, playing through places with their abilities, even though they weren't really used for a large portion of the game. It would have been nice if they had a dungeon for one of them or something, so they could put them to a little more use.
Dimitri was probably my favorite one, he just looked plain awesome. You could just ride around on his back and eat enemies and travel easily through the water. What was Dimitri, anyway? I'm pretty sure that I've heard that he's a type of dodongo, but certainly not any typical dodongo. Regardless of what he was, he was just plain awesome.
I think that Moosh is pretty close to my favorite as well, but I feel that his ability was a bit lacking. He was just plain awesome, though. He was a giant blue bear with wings, now how much cooler does it get than that? Both comical and pretty awesome in my opinion. His ability though... it was just meh. I know that Dimitri's swimming seems kind of plain, but all you really did with Moosh was fly over a few holes.