My favorite Dragon-type Pokémon is Rayquaza, by a longshot, both by design and by battling prowess.
Cool snake-like creatures have always fascinated me the most out of anything else. There's just always something intimidating about a giant serpent that makes me love them.
Let's take a minute to bask at Rayquaza's stats. Base 150 in both offenses means that it will hit hard on both sides of the spectrum, and combining that with its massive attacking movepool, Rayquaza has a plethora of options available for it. Base 95 speed is good enough for it to outspeed certain Pokémon and take them out, but at the same time it's not fast enough to outspeed other faster threats that can take it out. It's kind of a perfect balance to me, and its speed can even be boosted by Dragon Dance, one of my favorite boosting moves. While not impressively bulky, base 105/90/90 defenses are enough to allow Rayquaza to take certain neutral hits. Looking past the 4x weakness to Ice and weakness to Stealth Rock, Dragon/Flying is an amazing offensive typing, allowing its STAB moves to tear a hole into every type in the game for at least neutral damage, except for Steel.
Need I also mention Rayquaza's impressive Mega Evolution? I like to compare it to Deoxys-A, because they both have the second-highest base offenses in the game at a base 180. Unlike Deoxys-A, however, Mega Rayquaza has better offensive and defensive coverage with its typing and a hell of a lot more bulk, but with less speed. Delta Stream further improves Mega Rayquaza's bulk, as it removes its weakness to Rock, makes it resist Electric, and lessens its weakness to Ice. The best part about it would HAVE to be the fact that it doesn't require a Mega Stone! As such, Mega Rayquaza can go into battle holding any item it wants... Life Orb, Choice items, hell even Leftovers or a Rocky Helmet if you want to go bulky. Mega Rayquaza is probably the closest thing to a "perfect" Pokémon that this series has at this point, ever since RBY Mewtwo, I say.