Well, you know this one...
WOLVES! Bwahahaha! For "real" animals, it'd have to be canines in general. I'm a dog person. Though I do love cats and all animals really, but dogs...just always just been drawn to them. ^_^ And wolves, yeah. I love wolves a lot. I wouldn't mind being a wolf at all!
For mythical animals...mm...damn, that's hard! I love gryphons, manticores, phoenixes, and a good ol' fashioned unicorn and dragon. If I could be one, though, I'd be a gryphon. They just look badass and get the best of both worlds--flight, and they get to be a big ol' lazy lion-type and just...lay around and guard their gold all day. x3 Then again, unicorns are really cool. You get to be pretty and heal stuff, yay! Just gotta watch out for them virgins.