@Akemua—
So long as the series isn't nearing a conclusion, the mangaka and editor will not
want one girl to be perceived as the main love interest. On the other hand, it's probably hard for the mangaka not to have developed a favorite, and to allow that favorite to move a bit ahead of the rest, and more generally to allow some girls to be better positioned than are others.
That said, the real contest seems to be between Suzu and Chiaki, with Suzu in the lead. Kotone (the hypnotist) is intelligent, well adjusted, and physically beautiful; but she's been held-back by the writing, perhaps because otherwise it would be all too easy for her to take an overwhelming lead. Reiko (the Public Morals girl) got off to a very
bad start, though she evolved into a character for whom most of the audience might otherwise be rooting. Tanaka (the gyaru) has been held back simply by not making more appearances. Hayasaka (the track athlete) has appeared still less often, and Chiaki's brute strength gives her most of what advantage might otherwise go to an athlete. Nonoka (the mad scientist) is almost always kept behind those dreadful glasses, and she hasn't formed much emotional connection. Asahi (the advisor) is an adult, at least socially.