... which animal would you choose and why? Is that a major fantasy of yours?
My first choice would be a wolf or fox (the knotting; beautiful wild creatures), or an otter (adorable; writhing marathon sex session with many orgasms).
For otters, I'd choose a species where the male isn't rough on the female. In both cases, I'd prefer to be the male, since that's what I'm used to, but being the female would be interesting too.
Others I'd love to be: lion, zebra, parrot, fossa, weasel, polar bear, pig, koala. An eclectic list, I know. The main factors is how pleasurable and beautiful the mating looks, and very long or very frequent matings.