I assume Kaiten + Higanbana is stronger than Kaiten + Midare Setsugekka since Higanbana is the strongest single target move in the kit. Unless you need burst, and also a minute-long dot might not always work well with phase shifts.

Either way, it seems like you can do both since Kaiten has a short cooldown and thus you can buff each Iaijutsu with it and still have some filler Kenki left over.