My personal opinion would be Kushina. Not only is she typically cheaper and more common in events, but she is also more versatile in her ability to fit into many different lineups and will carry harder with harder scaling than Bee. Long fights will benefit Kushina more. Immunity suppression is a stronger status effect than super armor suppression. Kushina self heal is greater. Bee is also a very good choice though, so your team will be stronger no matter who you decide to choose.