Quick Answer: The chords in the drop-down are sorted by their musical conventionality, from top (conventional = more familiar results) to bottom (unconventional = unusual results).
Ranking of chords in chord selection menuLiquid Notes is based on a deep harmonic analysis that is able to read and interpret your MIDI arrangement like an expert composer does. Whenever you open a project, a track type classification will determine the different instruments and their role in the song, whereas the harmonic analysis will identify all correlations of notes between each other, define chord boundaries, etc. over your entire song.
This 'knowledge' gained from your arrangement enables the software to rank each chord on a virtual scale of chord substitutions ranging from very ordinary (conventional) to very unusual (unconventional) in accordance with listening habits in the Western world.
The drop-down menu for chords - which sits underneath the chord symbol - shows you all available chord substitutions for this particular chord. Within the drop-down menu, the substitutions are sorted by how conventional they are in the current musical context.
Consider the following example:
Here, you have three Am chords in sequence. As you can see in the drop-down menu for the chord Am selected, 'Am' is at the top most position. That's because an A minor chord is highly expected at this place.
For the same chord, at the bottom most position you can find an A major chord. That's because it's rather unconventional to use here, but yet conventional enough to be listed as an available substitution.
Note that for each substitution, there is a sub-menu that lists the available tensions for the corresponding substiution.
Experiment with different substitutions, and let your ear guide your choices!