Salamence > Dragonite > Haxorus > Gyarados > Kingdra > Scrafty > Latios > Tyranitar
I would like to reorder this list:
Dragonite >
Salamence >
Gyarados >
Haxorus >
Scrafty >
Latios >
Tyranitar >
Kingdra
Dragonite deserves more love than Mence because he's been the staple DDancer for about eight months now and he's not leaving anytime soon. With a plethora of options before him (Offensive DD, Bulky DD, SubDD), as well as an extremely varied attack pool (Outrage, Dragon Claw, Fire Punch, Earthquake, Waterfall, ExtremeSpeed), he is most definitely the premier DD user.
Salamence is a close second. With most Mence being the Choice Scarf variant in the past few months, DDMence is both powerful and unexpected in this metagame. With a Jolly Nature, one DD lets it outspeed the feared Scarf Genesect, which most teams rely on to do all the revenge killing. Mence wrecks it with a Fire Blast. Not only that, Moxie access basically assures that once Mence gets its first KO, the second and third will follow quickly. Earthquake is nice coverage and smashes the omnipresent Jirachi. As an aside, Hydro Pump in the Rain wrecks Gliscor, a normally solid check to Mence.
Gyarados is third, because once Rotom-W and Ferrothorn are out of the way, this thing sweeps. Like Mence, it also has Moxie, which deters the opponent from saccing Pokes to it because of the Attack boost Gyarados gains from the sacrifice. In Rain, a +1 Waterfall beats most anything that doesn't resist it, even doing well over 50% to defensive Skarmory. Earthquake and Stone Edge make for great coverage, with Ice Fang as a secondary option to hit those Grass types hard. Options in Substitute and Bounce increase its versatility, allowing it to perform a variety of roles on a team, as well as set up easier.
Haxorus is a beast, no doubt about it, but it's relatively frail and easily revenge-killed. Its disappointing base 97 Speed means even at +1, it falls short of outspeeding its eternal rival, Genesect, as well as Scarf Mence, Hydreigon, and Keldeo, among others. However, it's the best DD user when it comes to raw power. Base Attack of 147 is absurdly strong, and BW2 was nice to Haxorus; not only does it have access to Outrage and Earthquake, but it has now received both Superpower and Aqua Tail to add to its destructive power. It can be tough to set up, but if you somehow manage to achieve +2 Haxorus, game over.
Scrafty is a boss who knows no limits. Unfortunately, Tornadus-T takes a dump on its life, as even at +1 it doesn't outspeed and is OHKO'd by Hurricane 100% of the time. However, it's a very strong Pokemon in terms of defense, and setting up a DD is generally pretty simple. Once that's done, excellent Fighting/Dark/Ice coverage lets it tear through teams with ease. Drain Punch keeps it alive for a long time, Crunch is great STAB, and Ice Punch beats Gliscor all day long. Not as good as the top 4 DDancers, but worth a shot.
Latios has exactly one use as a Dragon Dancer, and that is surprise factor. Nobody expects a DD Latios, they're all either Specs, Scarf, or LO these days. However, its surprise value isn't enough to make it a good DD user. Base 90 Attack is extremely underwhelming compared to the 130+ of Dnite, Mence, and Haxorus. Granted, it still has access to Outrage and Earthquake, but they're better used on one of the top 4 DDancers that I listed. Draco Meteor is interesting, as it demolishes some common physical walls like Gliscor and Slowbro, but it's easy to see coming and not really worth it in the long run.
Tyranitar is trash in this metagame. Scizor and Breloom are on literally every other team, and with both of their priority attacks (Bullet Punch and Mach Punch respectively) OHKOing DDTar, there's a reason it isn't used much. Tornadus-T outspeeds Jolly max Speed +1 DDTar and OHKOs with Focus Blast or Superpower, so it has that to contend with as well. EdgeQuake is underwhelming in a metagame which boasts so many great offensive threats, and Terrakion does it better anyways.
Kingdra really sucks for one reason, that reason being that Ferrothorn, its #1 hard counter, is #3 in the usage stats. That's a recipe for disaster. Despite the prevalence of Rain, which doubles Kingdra's Speed for free, DD Kingdra simply does not pack enough punch to break through most of the premier defensive walls, and with two-move coverage, it's often hung out to dry by things like Slowbro and Jellicent. Really not worth your time unless you're carrying Magnezone and Gothitelle alongside it.
Well, that was a long-winded post, but I hope most of you can understand now why I put the various Dragon Dancers where I put them.
