Superior quality is obviously a matter of opinion, and it is the opinion of several influential chefs that Diamond Crystal is superior. The main thing they like about it is that Diamond Crystal is formed by evaporation instead of Morton's mechanical action, making it lighter and more delicate.

For example, Samin Nosrat, author of Salt Fat Acid Heat had this to say:

Nosrat also notes that Diamond Crystal dissolves much more quickly than Morton. “The more quickly salt dissolves, the less likely you are to overseason a dish, thinking it needs more salt when actually the salt just needs more time to dissolve.”

Other chefs feel the same way about Diamond Crystal, also noting that because its structure makes it less dense, they are less likely to oversalt things.

You'll notice that all of the quotes are related to using Diamond Crystal as a general-purpose cooking salt. Clearly, these superior qualities do not apply when measuring it for baking or using it for its original purpose -- kashering meat. In fact, for the latter purpose, there's reasons to believe that Morten's is superior as the denser crystals do more to draw out fluids before dissolving. For the same reason, one might hypothesize that Morton's would be better for BBQ rubs and similar applications (sadly, though, no data here; Diamond's trendiness is strong enough that Morton champions aren't publishing).

Superior quality is obviously a matter of opinion, and it is the opinion of several influential chefs that Diamond Crystal is superior. The main thing they like about it is that Diamond Crystal is formed by evaporation instead of Morton's mechanical action, making it lighter and more delicate.

For example, Samin Nosrat, author of Salt Fat Acid Heat had this to say:

Nosrat also notes that Diamond Crystal dissolves much more quickly than Morton. “The more quickly salt dissolves, the less likely you are to overseason a dish, thinking it needs more salt when actually the salt just needs more time to dissolve.”

Other chefs feel the same way about Diamond Crystal, also noting that because its structure makes it less dense, they are less likely to oversalt things.

You'll notice that all of the quotes are related to using Diamond Crystal as a general-purpose cooking salt. Clearly, these superior qualities do not apply when measuring it for baking or using it for its original purpose -- kashering meat. In fact, for the latter purpose, it's possible that Morton's is superior as the denser crystals do more to draw out fluids before dissolving. For the same reason, one might hypothesize that Morton's would be better for BBQ rubs and similar applications (sadly, though, no data here; Diamond's trendiness is strong enough that Morton champions aren't publishing).