Man, choice is easy. Horny model who is popular, horny actress, or horny pure and cute childhood friend? Two of these options are going to come with severe headaches later on in their careers.
Childhood friend wins everytime.
^ Some truth to this. Rio seems to have given up (for the moment), but as a girlfriend, Futaba/niPA would probably be a high-maintenance nightmare, and Shizuku is already giving off yanderish, "killer doormouse" vibes.
That said, Kaga has all but outright chosen Futaba*, and she's not only the obvious romantic lead/ideal, but also title character. So the attention devoted to Rio and Shizuku (and whoever comes next) just seems like a delaying tactic.
Cover of the final volume = Futaba in a wedding dress.
* ch 15: "If you can make the girl you like happy, that's reason enough!!"