I really have to limit this poll to my two favorite Dragon Pokemon or else I'd checkmark like, everything.
Latias - I love her cute design and she's dear to me. She's been my top favorite for over 10 years. I was fascinated by her when I randomly encountered here while surfing in Sapphire. I loved watching her star in Pokemon Heroes. She is my third highest-trained Pokemon after training her up to level 85 (the only other Pokemon I've raised beyond that, to level 100 both, were my Typhlosion starter in Gold nicknamed after my twin brother and my Talonflame flier in Y named after my uncle that passed away a few days before release). I've transferred my original Latias during each new generation. I like trading for more and having a whole team, though! Many friends have gifted me a Latias or even a shiny one. Love her to bits.
Dragalge - I really like this one because it's unique and is one of my favorite 6th gen Pokemon. It has a really interesting design with the kelp surrounding its body and unique in being a Poison/Dragon. I love its cry and bought Y just to have it. I caught its shiny form by using the fish chaining method and at one point had two Dragalge on my team (one being nonshiny and the other being the shiny one I caught a few weeks after release). I ended up raising both past level 60 because I like 'em so much.
I'd vote for just about all of the dragons as I like Dragonair, Flygon, Altaria, Salamence, Garchomp, Giratina, Haxorus, Hydreigon, Reshiram, Zekrom, Kyurem, Tyrantrum, Goodra, and Noivern.