I think you said it yourself, etcool... "there is not really a best salt to get"... regardless of tank type.
My advice is always to find a salt that is easy for you to get, and doesn't cause you any problems. That will be YOUR "best" salt! There are some salts out there that are high in calcium, but low in other things. There are other salts out there that are lower in calcium, but more balanced in other things. There's a free "report" on this site, that gives some basic numbers for different salts:
Aquarium Water Testing
While there may be some questionable results in it, I think it does give you an idea of the relative parameters between salts.
For a FOWLR
, I wouldn't have any issues recommending Instant Ocean - plenty of folks use it with no issues. I use the Instant Ocean "Reef Crystals", and have from day one. No issues from me.