Given that the metrics of the fonts under comparison are going to differ and this could impact legibility of glyphs, it might be useful to display some of the metrics values next to typeface names.

For example x height, cap height, width. These general design choices may help to explain why some legibility issues are better handled in some fonts than in others, particularly as you get to small sizes where a pixel or two of light or dark may be added here or there to distinguish characters based upon these metrics, whereas they cannot for fonts that do not share the same metrics.

Can you access these data in the OT tables?