I think of salt as I do tomato sauce (some call it gravy). It all depends on what you were brought up on, and so that's the one you end up liking and using. And that particular brand of salt ends up being the "best" salt for you. That said, I did start with Instant Ocean Reef Crystals, but found swings in alk/calc too high, and switched to plain old Instant Ocean....the best salt for me!
As far as changing brands, just do it with your routine water changes, using the new salt. Just monitor your alk and calc (and mag), and adjust as needed to stay within your desired levels.