It's difficult to declaratively and definitively say which are the three main chords, as they all get a turn from time to time, though admittedly some more than others. C would have to be up at the top, even if only for having been deigned the harmonic centre of tonality by Western musical standards. Perhaps, then, fanning outwards, from least to most complex in terms of accidentals would be the logical way to go in terms of determining main chords in music.