When I was around 10 years old, possibly younger, I typed out a mini-encyclopedia about dinosaurs, including details on every dinosaur I could find out about in roughly 10 books. I loved dinosaurs.

Having said that, I'm not sure which my favourite was - I just loved them all. There were some I favoured - Ankylosaurus, Brachiosaurus, Deinonychus, Styracosaurus... although it was not actually a dinosaur, I always liked Dimetrodons, too.

Mitto: http://en.wikipedia.org/wiki/List_of_dinosaurs