Well…‘good’, ‘better’ and ‘best’ are all subjective! I know you’re probably hoping that I’d be able to give you a list of qualities/ attributes to look out for, but how can you quantify the beauty of rare gems into a checklist?
Unlike Diamonds’ 4 Cs, coloured gemstones have a life that cannot be charted but the best stones generally have the magical trio of good colour, cut and clarity, with colours which are bright and lively, with high saturation (if they’re not meant to be grey) and pure hues (eg. grey Spinels with no secondary hues or pink Tourmalines without hints of brown). Generally, the medium tones are the most sought after, and thus the most highly prized, but people like what they like!
The only way to tell if a gem is ‘better’ than the next, is to put them side by side and compare them. This is because human brains don’t have colour memory, so we wouldn’t even be able compare two stones seen on two different days accurately. Make sure that your jeweller has a full range of coloured stones at different price points for you to compare and see the difference for yourself.
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https://www.medicaldaily.com/memory-color-shades-why-human-brain-struggles-remember-color-336396