TBH my favorite is the witch. Let the Harem of 7 become a Harem of 8 please, and the seeds are already sown. Realistically they'll need her help to fend off the MC's home country anyway. It seems pretty imperialistic.
Interestingly for this sort of story, every single girl is great and I like all of them. Normally you have a few dud characters. Maybe it's just because it's not a school romcom but such a unique situation that it's relatively refreshing.