Choosing the "best salt" is just about the most controversial topic you can post on. It's almost a religion with some people.
With out trying to start a "salt war", I can say that I have used Marine Environment salt for years. I like it a lot. That being said, I don't know of any way to prove that it's better or worse than many other salts available.
I know a few salts that I will not use, because they don't mix up to anything close to correct levels, or had other problems. On "other brand X", not mentioned above, had problems with the magnesium level after mixing, and couldn't maintain correct calcium levels.
Also, keep in mind that almost everyone posting here is a hobbiest, and they have no scientific way to demonstrate why one salt is better than another. It's simply what they observe in their own tanks.
In addition, look at the number of brands of salt out there. Even people with many years of experience usually have only tried a few brands.