Whey will taste better, but if you have a dairy allergy and can't have whey the vegan is fantastic. It really comes down to the consumer and if they can or can't handle dairy. Hence why the Vegan is made for those who have a dairy sensitivity.
The sludge has been the best thing for me while pregnant and having gestational diabetes and Ghost being low carb, low sugar is the best. Do you plan on doing any baking with the vegan or just the whey?