I also think that of all the girls thus far Kinosaki and Ham-waifu are the most distinct. Kinosaki because she's from 'before' his quest, and Ham-waifu because she was already in love with (or at least greatly admiring) Gero before he did something to help her out. His rescue of her didn't create her feelings, just solidify them.
Hamster is definitely nicest as overall. I'd say with the whole "doctors only marry doctors" thing, as they are both specialists and know all the issues with their field of work, lifestyle-wise I'd say they also are the best match. I agree with Kinosaki being the only real contestant, and the fact that Gero's entire arc of becoming more sociable being primarily due to Kinosaki's guiding influence to be pretty cute. I just hope the author resolves the relationships Gero has with Kinosaki and Hamster in a fulfilling way, as a sudden breakup between Hamster and Gero would be weird, and similarly there needs to be a bit of a build-up to how or why Kinosaki would separate most ties (except maybe friendship) with Gero.
I would hate soem half-assed harem route to take place.
Personally, I see either: 1, Kinosaki bringing up background information to their own issues or desires which make a relationship with Gero completely impossible which by process of elimination, Hamster wins (Gero&Hamster),
2, Gero never developing feelings for Kinosaki, likely similar for Kinosaki due to the line she drew between them so Hamster is the remaining lead (Gero&Hamster),
3, Hamster and Gero clarify their feelings towards each other, then Gero cleans up the messy relationship with Kinosaki (where Gero and Kinosaki do have something for each other, but move on past that to a more stable friendly relationship)
4, Hamster has some severe crisis that prevents a relationship, and Kinosaki supports
both Gero and Hamster through that, during which Gero gets closer to Kinosaki.
5, Gero is truly vulnerable and needs others' help for some new reason. Kinosaki gets closer to them while trying to help them. Hamster, for whatever reason, isn't able to do the same role Kinosaki does.
6, Hamster changes their feelings to not be romantic for whatever reason, and it turns into either guilt, admiration, or idolization (or a combination of that). Then proceeds to turn down Gero as a result (I don't think this route is likely).
7, some unforeseen route or a combo of the previous that I can't think of.