I've used so many over the years and have settled on Aquaforest. I never noticed any brand that made any considerable difference in terms of health of animals in the tank, I think it just depends what parameters you want, cost, convenience etc. Here is what I found with the ones I used:
Reef Crystals:
Good price and parameters, no negative issues with results in the tank inhabitants, easy to find everywhere locally. I stopped using it because of the brown crud it left in my mixing containers which led to more work for me cleaning.
Fritz Blue:
Good Price and results, but it didn't work out for me because I premix my salt in drums and store for couple weeks before using. I found the alk dropped quite bit if I stored it more than a couple weeks. If you don't have to store it, this would be a good option IMO. Mixes pretty clean. I've read some people say they ICP tested this salt and sometimes the parameters aren't consistant. However, as someone else mentioned earlier...when your changing 10-15% those are going to have minimal effect overall on your tank parameters.
Tropic Marin Pro:
Was a great salt, but the cost has risen so much so I went elsewhere. The time they had those bad made in Turkey batches and had limited availability afterwards pushed me away from them. It was a great salt though.
Aquaforest Reef: Found it mixes super fast and as clean as Tropic Marin. Parameters are good and seem to hold pretty well when in storage for over 2 weeks. Price is fantastic when on sale, and it goes on sale at least few times year at
BRS. I just stock up when the sale comes. Only negative is there is no where locally that sells it, so availability can be an issue for me if I don't stock up.
These are just my personal experiences. Do what you will with it. Good luck!