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IMO Gin wins comfortably. Soifon is a short-range fighter and you need long-range attacks to defeat Gin's bankai. Soifon's bankai is destructive but she only has one chance and IMO it's pretty hard for her to hit small targets with it unless she catches them off-guard.
Soifon's bankai, per usual, is practically worthless here. Sealed blade probably will get cut through, and her shikai isn't the best at blocking. She'd basically be forced to dodge everything, which she should be able to do easily enough. Problem is she'd be forced to fight close range as her shikai is her only option. It's close due to her speed, but Gin might have an edge there as it's easier to keep it ranged.