I feel like of the entire cast of characters Evangelion offers Misato is the one who most has her shit together. Is shd perfect? Absolutely not. However, she is a functional adult with many practical life skills. Let’s not forget that she was able to fix a totaled car with a few stolen parts and batteries. As well she seems to be fun and energetic yet sweet and vulnerable. By virtue of being the least broken person in the series she is thereby the most optimal choice.
Though between Rei and Asuka specifically I’d say Asuka is the clear choice. Rei is hardly a functional human being and seems to be for the most part devoid of any substantial personality. Also shd left bloody bandages on her apartment floor and that’s just gross.
Asuka on the other hand, while a bit of a cunt, can be reasonably managed with a bit of work. She seems like she’d be high maintenance but overall could be a lot like a more feminine Misato if she would open up and calm the fuck down.