Most important IMO is third-party testing along with published results. Concentrating nutrients also concentrates contaminants like lead and PFAS, and many powders have cocoa, which is also notorious for lead contamination.

I second this – it’s a much bigger project but this is the criteria that I care about most.

Whether contaminants are also concentrated depends on the concentration method that is used.

For example, the protein concentrates from whey or milk are obtained by just two filtrations through filters with different pore sizes, the first coarse filter retains any larger particles, including bacteria, while the second fine filter retains the protein particles and passes the water with lactose and fat and also with any contaminants that are soluble in fat or in water.

Thus the protein concentrates from whey or milk normally have less contaminants than in the whey or milk used for their production.

Good point. FWIW, the "It's just" product claims to be tested for heavy metals, microbiotics, and "purity".

(Not associated with the brand or with any vendors, it's just the brand I've been buying.)

Seriously, why is it so hard to find a protein powder that doesn't include Stevia (or its distilled, chemical name). I don't care about my protein powder being sweet, but if it's gonna be sweet, give me some raw sugar. Stevia is bitter and ruins the whole shake.