For me, it will always be the original trio of dragons, Dratini, Dragonair, and Dragonite. They're all adorable, beautiful Pokémon, and I always loved the idea of Dragonite as this sweet, friendly Pokémon who also happened to secretly be a badass. Much more interesting than some of the more "stereotypical" takes on dragons we got in later games.
It still annoys me that Dragonite has no Mega Evolution when all of the other pre-Gen 5 Pseudos do. I'm hoping and praying this is because Mega Dragonite will be Dragon/Fairy, and they specifically want to release it alongside Mega Hydreigon for a "Good Dragon vs Bad Dragon" contrast.