Everyone's gonna have an opinion on that one.
It's not so much that salt mixes contain different elements from one another. They are essentially the same, especially in the macro-element department (NaCl, Ca, etc.)
There have been comparitive assays done by several independent sources (viewable on-line) which will let you know which trace elements appear in what quantity in various salt mixes. Frankly, I find them to be a bit tedious to read and have always come away confused as to whether ~10% more/less Strontium, Beryllium, Gold or whatever in one mix compared to another actually makes a difference. IME, having used numerous brands, it does not.
Rather, I use the same salt mix that the LFS I most often frequent uses and run at the same salinity they do. It makes more sense to me to ease the acclimation process for my critters than to worry about whether or not they're getting enough of something I can't test for anyway.
Doing regular water changes is, IMO, far more important than which salt mix you use.