Hanako, Why ?
1)Always nice to be with your favorite girl.
2)She is one of the girls who isn't disadvantaged for a survival situation: I'm sure the others can be useful but...even if the premise is that we are not really in trouble; Lilly would be completely paralyzed by his blindness, Emi's prostheses may become damaged /not be usable in the sand and jungle, Shizune's deafness can be dangerous for herself, Rin can not really help in the construction and can still be dangerous for her in a survival situation despite her agility.
No serious reasons to judge Misha more capable than Hanako and it's the same for the others : the fact that Akira is cool don't makes her more suitable for survive, Kenji is not a good choice because of his legal blindness and he don't seems to have real useful skills, Jigoro looks sporty (that does not necessarily mean much) but is not the most willing to help, I don't see why Yuuko would be more likely to be useful than Hanako, the same with Mutou and medical knowledge of the Nurse is not very useful without medical equipment. (if you get malaria, he don't will magically curate you)
The benefit of Miki's sportiness don't worth her disability, and there is no proof that she has survival skills.
3)I don't agree with the assumption that Hanako could not psychologically endure the accident : The Hanako Route proves she lived terribles things, can endure pains, and that she does not suddenly go mad or something; Actually I am more confident in her than in the girls who have always had their disability (Lilly Rin, Shizune)
because they do not seem to have experienced something like that. (For Emi, her accident is enough in itself; Hisao could be a good choice for this if there was not his heart disease combined with the absence of his medication)
Of course inexperience does not mean that these three girls necessarily would breakdown, but it is no more improbable than Hanako.
Thus, assume either is a pure assumption but I am inclined to the Hanako's mental resilience theory. There is nothing to judge the mental resilience of secondary characters : except perhaps Kenji and Jigoro whose their behavior (Both have too many unresolved emotional problems,
where Hanako is internally very solid) seem more unfavorable. (Yuuko is stressed for nothing but it's no major, the same with the little apathy of Mutou.)
4)Her kindness would be the best motivation to stay alive, not really the easiest relationship but the most stimulating and comforting. (The danger would be the white-knighthing, which could oppress her if she finds herself alone with a white knight but the situation could also provide an opportunity to really understand her, or sadly enhance the appearance of a "damsel in distress"
even for her own gaze : i don't think it's possible to override this barrier if herself don't believe it's possible or if she don't wants it happens; she is no so passive in the hisao-hanako dynamic)
And she surely find good games to don't get bored.
(a deserted island is soooooo boring, I would don't be unhappy to play tiles game beach edition, or find shells to play chess with her; talk about books we have read,ect...)
Overall, I think it is very nice to spend time with her even with nothing. (to a lesser extent also Lilly, drinking tea is not exciting but the presence of these two girls is simply nice)
I don't think I would get on with Shizune, Emi, Rin, Misha or the others as well as with Hanako.