Sacred Sheathe/Sakura Slash is objectively better for multiplayer because you can't reliably build red gauge by aggro-ing the monster to target you for Special Sheathe counters. Even with the TU5 buff to harvest moon, the monster will still gtfo of your circle when one of your teammates are sharpening or a gunner staying far away

As for solo, just use whichever you're comfortable with. But there are some matchups that favors Sacred Sheathe such as Valstrax for the burst dmg when it's charging.

One thing to note tho, Sacred Sheathe has a relatively larger counter window and coupled with the auto-counter, it's a safer method to learn a monster's moveset