Why is Dragonite not in this poll? He's clearly superior to both.
Dragonite bests Gaburaisu in everything but Speed and HP. His defenses and Special Attack are much higher making his Dragon type moves much more potent against other dragons (since Dragon is weak to Dragon)
Dragonite and Salamence are close in stat, but Dragonite's defenses are at least 10 points higher in Base, while Salamence's attacks are only about 1-5 points greater. Salamence is also faster. HOwever, due to it's low Sp.Def Dragonite can kill it easily with Dragon moves.
Dragonite is also the only one out of the three able to use Ice Moves(Ice Beam, Blizzard, Mist, and Haze) which can be just as potent against them. Although he's slowest of the 3, he boasts higher defenses. Set him with a Dragon Dance/Agility, Dragon Claw, Earthquake/(stab)WingAttack, and Ice Beam/Flamethrower. and You have a Superior Dragon.
or just for fun. Mist/Haze, Meteoric Swarm, Earthquake, Stone Edge. MSwarm with out any setbacks.