Dragon would be your best bet for now as the other two are relatively gimped.
But in short, you choose
Dragon to focus on DPS
Harmonious to focus on Debuff
Drunken to focus on Off-tanking

The way monk skills are classified is rather confusing.

There are SIX classifications you can see on monk's skill list:
Dragon style, Harmonious style, and Drunken style.
Dragon Mastery, Harmonious Mastery and Drunken Mastery.

The "styles" are general - every monk can use them, while the "mastery" skills are specific to each discipline.

For example Thousand fists is drunken style, which every monk can use, but Jeering Kick is drunken mastery, only available to drunken monks.

Feign death is a general skill.

Dragon is no less broken or gimped than the others.
In truth, Harmonious is regarded by most as being the most complete and least gimped right now.

Dragon:
Storm stance damage is low and doesn't stack with secrets.
Dragon stance does nothing.
Stone stance only adds about +5% mitigation.

Harmonious is capable of doing as much damage as Dragon, possibly more, through use of Tiger stance and it's debuffs.
The only advantage Dragon seems to have is that it requires less effort to do it's damage (You don't have to jump between stances, and you don't have to debuff first), so it may be more consistent.
But Dragon losses out on the powerful evasive stance of Harmonious and the fairly useful jin gaining stance.
Dragon also loses out on the added team utility of debuffs.

That's outdated information. Storm stance DOES add nice damage now - compared to before. Unsure about stacking issues. Dragon stance is now actually useful for downtime, though it is still not worth keeping up in group fights. And ONLY 5% mitigation is relative, when my normal mitigation is aout 15%, that's an increase of 33%.

Stating the tooltip exactly appears rather pointless, as the tooltips appears to be mostly broken to be fair, abilities usually do noticable more damage than they should.
At 50, you'll have:
- Celestial Kick of the Masters which is another flying kick chain, dealing slightly more damage, gives 2 jin (even though tooltip states 1, so it's a better choice in all ways than tickling heart technique).
- Find the Center that increase your parry and block (says a bit on how through check on monk skills have been) by 100% for 20 seconds, 20 minute reuse.
- Diamond Body II, which is pretty much like rank I with a possible higher AC buff. Due to the reuse and uncertainity on what mob abilites are actully using proper counters, I never saw enough reason to test it. For those who haven't got rank I, it's a 30 minute ability which boost ac with a small amout (0 according to tooltip - but it does increase the one time I tested it and some poison thingie didn't wear off! ;p) and suppsoedly cleanses diseases, poisons and curses every second for the duration. An ability with 30 minute reuse that's dependent on that develeopers has properly flagged abilities isn't going to see much use.
- Withering Palm I. You get this at 46; I don't see why a supposed trademark ability comes this late. It's a very nice ability, taps the mob for 10% damage (1 minute duration on yourself, 20 second on mob for 6 jin). The ability supposedly deals 75% melee damage + 300ish, but hits quite a bit harder.
- Eagle Claw scales up to 24 seconds at highest rank (as patchnote said), Deadly Adder likewise to 32. Their damage or effect dosen't change in any unpredictable way.
- Steal the Wind. More than minor changes in the damage, nothing exciting happends on it.
- North Wind series. Obtained at 38, followup added at 42 This line fills no purpose at all offensively; it was upgraded to a 30 second duration (1 minute reuse) which makes the first ability (lowers mobs damgae by 75) quite decent, but the second finisher at rank II (mob takes 300 damage when attackign for 30 seconds) dosen't really compete with a single flying kick. It's like deadly adder hand, a useful ability when you want to reduce incoming damage (but this can't be maintained for long); but hardly for damage.

There's some more abilities, but seriously enough though, most abilities are quite lame, I found myself using more or less exclusively:
- Eagle Claw.
- Withering Palm once it's obtained.
- Celestial Kick.
- Ashen Hand.
- Thousand Fists.
- Cresent Kick.
- Feign Death.
- Bumbi-bear bouncy.
- Mezmerize ability (even though I nearly forgot about it when entered Raz Inkur)
Any other ability wouldn't get used except in situations where I set myself up for them (all defensive abilities occur global cooldown, so they aren't all that accessible when doing FD stunts or speed bursting with bouncy-bouncy). Pretty sad.
An alternative to what I do is not use AH but rather boost your party with Jin Surge every 20 second and rely on Withering Palm. It probably has a higher damage output (Jin Surge V is approximitly +400 damage on next attack) on a full group, but it's a preference I suppose. Still, the amout of abilities used is staggeredly limited.

The critrate from level 50 (+30%) along with fists makes you do really nothing else than crit. It's press button to trigger a finisher, then do finisher, press buttons again until you get finisher. Due to the flying kick chain generating 4 jin at 50, it can single handedly maintain a ashen hand (which tends to crit, leading to another flying kick chain etc) with the odd Withering Palm. Generation of Jin at 50 is rather high for all styles, in particular for harmonious (mostly from the tripple finisher which comes up ALL the time) so AH/Jin Surge/Withering Palm spam isn't out of the picture.
Harmonious is slightly weaker than Dragon after the stance fixes until 50, where it bursts into power.
Harmonious stances evolve much more dramatically and all abilities sum up nicely at 50, where dragon dosen't really get a burst in the form of stances at 50, and the 50 style specifics are cruel jokes.