I'm a simple man. I see 5k roll with ticket, I buy. I got dupe Onci, Onci got another equipment slot (her skill is already maxed), and for the rainbow... Yet again, not sure who to pick.

Horse Chestnut - fits quite well into my current setup - pierce type with debuff and blunt weakness, builds into debuff team for Kerria later on. But I have mixed feelings about her waifu levels. Didn't like her that much at first glance. But now the more I think of it, the more she grows on me.
Sensitive Plant - really good waifu-wise, she's just broken, and makes a fine addition to every team. But, to be honest, I don't really know where to put her in my current setup.
Easter Cactus - middle ground of above two. Just like Chestnut, fits into main team - Kerria and Alpinia are almost always topped off, so less possible targets for heal/revive=easier to play around it, with waifu levels of Sleepy-chan. And I heard her H scene is epic, I simply have to see it. But I already have 4 slice rainbows. And I'm not sure if she's really worth it, as she's only okay-ish outside of her ability to (sometimes) revive.