Double Ichimonji is probably the best sword skill in game.

[CoconutMan]

Destroying Every single boss by punishing them after every mikiri counter.

[JuiceySpice]

Yep, very good output, decent recovery, and no emblem cost

[PCF | Tanasinn]

Yeah I made on a thread on this too, last week or so. There are a few contenders, such as:

• The last Senpou Temple skill - It makes you jump over sweeps and does more posture damage than just jumping on their heads. Apparently it's a significant amount of posture damage but I haven't used it enough to really understand when it shines since the enemies just block the extra hits when I do it.
  
• Nightjar/Reverse - The utility they (apparently) offer in terms of gap closing and gap creating is quick and includes a strike.
  
• Shadowsneak - Apparently it's an unblockable gapcloser.

I think there was another skill but people suggested but yeah Double Ichimonji is still hands down the best. Recovers your posture, damages enemy posture on block, deals vitality damage and posture damage on no-block.

Final edit: here is the thread if you want to look at the replies regarding the other skills I mentioned:
https://steamcommunity.com/app/814380/discussions/0/1771511442688251811/

I tried to get as many answers as I could regarding why they think their skill is better than The Ichimonji set.

[Samurai]

I used the tomoe skill (forgot the name) you get early for scales for most of the game with ichimonji only for certain encounters.

The monk skills are too long to be any useful on boss fights and the rest i didn't really unlock until ng+.

In ng+ i used the lai skill for pure damage output.

[Leoscar]

I have to agree, there are a lot of useless special moves in this game. This one is one of the few that are useful. The second hit is meant to interrupt the ennemy trying to hit after taking the hit and it actually works. All of this for free.

[Bishop]

Shadowfall is better in some situations I think. it could be so stupidly OP if it didn't cost any emblems though. But still is auto win against most minibosses.
Ijimonji is good but it requires proper timings.

[CoconutMan]

Originally posted by Oberst Heavy:

I used the tomoe skill (forgot the name) you get early for scales for most of the game with ichimonji only for certain encounters.

The monk skills are too long to be any useful on boss fights and the rest i didn't really unlock until ng+.

In ng+ i used the lai skill for pure damage output.

Monk skills are pretty good against enemies who turtle. But they ain't got nothing on Ashina Clan techniques.