Personally I use Reef Crystals.
Like Tank said, are you going FOWLR or Reef, as it will help sway the opinions.
AWT did a lab grade analysis on a dozen or so different types of salt. This doesn't paint a complete picture, but it is a very good reference of what to expect in my opinion.
http://aquariumwatertesting.com/AWT_...lysis_0208.pdf