A Brontosaurus!
They were my most favorite animal when I was little. Infact, it would be neat if any dinosaur was brought back out of extinction. I wasn't the kind of kid who played with barbies and dolls, I played with dinosaurs!

Though in reality, it would never ever work. Humans have taken over way too much land for dinosaurs to live again. Heck, its like we can hardly provide for all the humans on earth these days.