Question one: does your target programme specify required subjects? Requirements differ across university programmes — some list specific electives, others only specify how grades are counted. These requirements can change from year to year, so check what the institution has published for the relevant admission cycle. Start here because it eliminates certain combinations outright: however strong the interest, you cannot apply without the required subject.
Question two: how have you actually performed in these subjects? Not one test score, but the trend over time. Electives run for two years, so the starting level and the ability to keep going both matter. If a subject is only holding up because of heavy tutoring, ask whether it will hold up without it.
Interest is question three. Its value is that it sustains effort over two years, not that it guarantees grades. The useful question is not 'do I like this subject' but 'will I keep working at it when the material gets hard and my grades dip'. An answer to that is a sustainable choice.
One more that is easy to miss: the combined workload. Three electives that are all reading-heavy or all writing-heavy will collide in the run-up to exams. Estimate the routine homework load of the whole combination, not just the difficulty of each subject in isolation.