Considering I think I must've been a cat in my past life (not that I believe in reincarnation), I'd probably go with something that doesn't do shit. Like a fish in a tank.
Well if being reborn as an 11 year old Japanese girl so that I can audition for Morning Musume's 12 gen isn't an option...
And considering that many animals are losing their habits or being hunted to extinction...
And also considering that pollution in the oceans is still increasing...
I'll go with a dog or a cat... And not a stray or an abused one. Just one who can be pampered by a rich family... Well except for those tiny dogs that get carried around in purses like an acessory rather than a dog...
Thinking about it... Cat might be a better option. Much more can go wrong if I am a dog. I don't want to be too dependent on humans. As a cat I can lay around all day or sleep and no one will bother me. Plus I don't have to beg everytime I want to use the bathroom.