I guess it depend on your team. If you want debuff to support a good offensive girl (like Kerria andher clones), go for White Tulip and her +40% ATK. If you want to support more defensive girls (espacially if you have one with Evasion+Provocation), go for Cypress.
I don't think there is someone better. But if you want pure Debuff, Sedum is a good choice too: https://flowerknight.wikia.com/wiki/Sedum. Perfect to support Evasion girls.