Which Loki to use?

I can't really see an attack bane being all that useful for her if you have another IV set that touches some of her "least important" stats.

Unless you're building Loki to be a mage tank, then her resistance isn't really needed. Her main role is support anyway.

It depends on how you use her. If you give her Dazzling Staff the RES bane won't matter. I presonally would go for the +DEF/-RES Loki. You can even minigate the bane and help her Thokk effect with the HP/RES 2 S.S..

Hmm, very interesting choice!

I mean, she usually won't kill stuff outright so I don't think -atk is a big deal, and I like +HP. But I would prefer not to have -atk because her prf has wrathful on it. Both IVs are good. It's a matter of preference. I probably would go +def -res... probably.

I've written more here
https://fireemblem.gamepress.gg/q-a/i-pulled-lokikliffowain-what-do-i-do