I know there have been discussions about how some Pokémon start out cute, and then evolve into something tough and scary-looking, but what I'd like to discuss here is something a bit more specific: Do you vastly prefer some Pokémon's earlier sprites over their later ones? (Example: Perhaps you like the Cyndaquil sprite a lot more than the Typhlosion sprite). If so, which ones, and why?
In my case, I think Squirtle and Gible take the cake.
Squirtle starts out cute, and I like its sprite well enough, but Wartortle is really cool-looking. It has wings on its head and tail, and its body is still curvy and graceful, like Squirtle's. It looks like a cool creature from Greek mythology or something. But when it evolves into Blastoise, it looks like a blue King Bowser with pipes sticking out of its shell. (Don't get me wrong, Blastoise is still neat -- just not as cool as Wartortle, which is too bad, because the final evolution is of course the strongest).
When it comes to Gible, I think Gible is really cute, as well as cool-looking. His DP animation is also really fun to watch. After that, though, he evolves into what looks like a hammerhead crossed with a T-rex, bred with a kangaroo! Once again, Gabite and Garchomp are still neat in their own right, but not as cool as Gible.