I always say that if the "Intrinsic Nature" spell Nysander does in Luck in the Shadows were used on me, I'd be an emu. I just *am* an emu. With some dyed feathers and rhinestone bracelets and tacky eyeshadow. (Other animals that remind me of myself: ostrich, giraffe, macaw.)
Now if I could choose what to be, I think a blue whale, sperm whale or humpbacked whale would be awesome -- long as it came with superpowers to kill whalers or turn them to stone or something. Who wouldn't want to be the biggest animal on the planet, in the ocean, surrounded by friends and family?