I think Kurenai Summer, but I don't have Edo Itachi so I can't speak from experience using him. I think Kurenai might also be cheaper to get? Not sure 100% about that tho.

IMO Kurenai's mystery is better but Edo Itachi might have a bit more survivability as pos 2 since he can dodge chase. Kurenai can chaos her attackers but sometimes they will be immune so they will continue the combo. But her mystery is good, causing suppression and immobile. Sure the immobile can be cleansed easier than Itachi's dream state, but the thing is once that immunity is suppressed, even if they have a healer on their team, the immobile will be removed but the suppression won't I'm pretty sure (unless overriden by Fire main's shields, I think.) So that same unit could hit her again and get chaos'd again. Reducing chakra to 60 is also really nice for Kakuzu teams and blitz mystery teams in general. I will say that most teams don't have all immune ninja and chaosing 3/4 of a team can be really satisfying.

What would be really fun would be to use Itachi and Kurenai together lol.

Hope this helps in some way!

EDIT: Actually, if you have enough for him, New Year's Hashirama might be a better option than both of them. I got Summer Kurenai and then he came out like 3 weeks later and I was like "bruh" lol. His mystery does pretty much the same thing as hers, but he's also immune to debuffs and recovers health when attacked similar to BT Gaara. That's very nice on a pos 2 ninja, considering Itachi and Kurenai are kinda frail. He doesn't have as much cc as Kurenai outside of his mystery but he does have that passive that increases chases and that could be very helpful as a support for Kushina, who can reduce her cooldown on her chase. Plus the mystery cost increase on his chase which is great paired with his mystery limiting chakra to 60, you can limit how much your opponent uses their mysteries in a way that doesn't care about immobile/chaos/immunity to debuffs.