There's no problem with availability on the Reef Salt from Seachem that I have heard of, don't know who told you that, but we have pallets worth. We run out occasionally when someone gobbles up a whole pallet, but that's usually only for a couple days at most as we have a local distributor that keeps +/-10 pallets of it on hand. No worries there....
As far as whats "Best" that's a whole other ball of worms...
Personally, I use Tropic Marin, as it mixes up perfectly to keep things in range on my system without having to doctor up the water before I use it, and I have never seen anything build up in the bottom of my mixing vat. Ill pay a little extra for that convenience alone.
The other thing I like, is that it hasnt changed a bit since I started using it, many of the others have radically changed their mixes as cost and availability and shipping costs of certain salts changed, so pretty much all the salt tests that were done more than say two years ago, you can pretty much ignore at this point, put your trust in good test kits, not the internetz.
One neat thing that Seachem does with their Salinity salt is they attach a lot# to every bucket, and you can look that lot# up on a website to see the test results from tests performed by the University of Georgia.
Seachem and IO (Seachem Reef, Seachem Marine, Instant Ocean, and Reef crystals) are made in the same location (Aquarium Systems), (the Seachem Salinity is actually made in Seachem's Stone Mtn facility, the reef and marine will be made there soon. There may be a slight slow down while they make that switch, but I doubt it would be anything felt on the retail level.)
DD+ and RedSea both come from Israel, as byproducts of the Saltwater Steam Desalination plants they use for their drinking water, it makes nice clean drinking water, and piles, and piles of salt daily. They both add some buffering and other tidbits, and mix it up. (Both work well, but I have had issues with consistency from lot to lot)
TM is mixed in germany, regular, pro, and Bioactiv. (Germans LOVE their chems)
Kent and Oceanic are made in the same spot. (Havent used either in years...)
Brightwell is mixed up by evil elves that like to inflict pain. (Ever gotten that stuff on sweaty forearms?)
ESV is made here in the US on the East coast. (Great salt! But I'm Lazy)
At the end of the day, all these salts will work well, how well depends on exactly what you are trying to do. Find one, stick with it, and only change if you have to, and pay more attention to keeping Alk, Cal, and Mag in shape, use good feed, and keep up with the maintenance as others have said, and it won't matter so much.
