Dragon might actually be the one type where I think the designs have gotten better over the years, and that's almost certainly due to the designers actually attempting to populate the type a little more and trying out concepts beyond 'European dragon'.
1: Druddigon - So, uh, I guess I'm a hypocrite for loving this European dragon? The raw gnarliness of his design puts him near the top, but his concept and execution place him at No.1 for me - he's partly UK-inspired, his stat distribution, movepool and abilities all marry with the concept beautifully, and he even gets hipster points in my book for being one of the less popular Dragons.
2: Tyrantrum - I'm a simple man, I see a Tyrannoaur Pokémon and I covet it. It's so on-the-nose it comes close to tacky fanservice, but I've no doubt my six-year old self would have loved it above all others.
Joint 3: Hydreigon and Guzzlord. Dark's a very interesting and balanced type competitively, and I like that both of these are meaner than the slightly boring European dragons. Guzzlord's design is a little cartoony for my tastes, but he also enjoys less love from the fans, I think, so it's a wash in my eyes.