Animal: Falcon, orca, or crow, but I do not think, that I would just want to be an animal, and that is all, it would be much more interesting to have possibilities to turn into animal, and not only to have experiences, but also at the same time have the enhanced human intelligence of sorts, and use it for many more interesting things to do, that in real life are of course both unimaginable, and impossible.
Fantasy:
One of many things: Dragon with similar abilities, that dragons have in Inheritance cycle.