First of all, why do you even have a Kartana under rain? Kartana has no business being on a rain team but I won't go into detail on that because that's not the question
The simple answer is that none of those is the best way to use Kartana. There is almost no single best way to use a Pokemon if all its sets are equally viable. It would all depend on your team
If you are using a choice band Kartana, then its role is as a wall breaker. This one requires anti metal birb support so that Kartana can freely use its stabs. The disgusting Magnezone is a good partner because it can get rid of both metal birb and durian for Kartana
Sd lo Kartana mostly follows the same rules as band except it has more freedom for its moves. Unlike band however, this one requires slightly less support because it can freely choose moves. Instead, what it needs are stuff that can handle the faster threats like Koko and Dragapult, which is also something band needs
Finally, scarf Kartana is different. It acts as both speed control and cleaner. It should be preserved for a late game sweep and clean up after the enemy team is weakened. This one would focus more on revenge killing since scarf Tana is the fastest common scarfer in the tier. It also needs similar support to choice band. Also, contrary to what the other answer says, do not use adamant Kartana. You do not want to be unable to revenge kill Garchomp
In the end, it all depends on whether your team needs a cleaner or breaker
