Use 'incommensurable' when comparing feelings or experiences that lack a common measure. The joys of parenting and solo travel are incommensurable.
Pro Tip 2/3
Non-quantifiable aspects
'Incommensurable' suits discussions where things can't be quantified, like emotional states. Her talent and passion for art were incommensurable and defied any ranking system.
Pro Tip 3/3
Subjective experience
Expressing personal sentiments or individual experiences can be conveyed with 'incommensurable'. The beauty he saw in the sunset was incommensurable with any prior sight.