Good choices, he's probably a combination of these. He was called a useless reptile by Hiccup, his eyes move like a cat's, he's black and hangs upsidedown sometimes when he sleeps, and he plays fetch and turns three times before laying down on the groumd

Cat fans think Dragons are Cats.
Toothless is a reptile, so he's a lizard.

I see him as a combination of a bat and a lizard mostly! (I am a huge cat fan though xD)

meow^^ he's a kind of all. cat's eyes, dog's devotion, bat's wings and lizard's body