There are huge debates on this....
What do you plan on doing w/ the tank?
if you're going reef Tropic Marin is the way to go. I know al alot of other people really like Kent and Oceanic as well. If it's a fish only tank I'd go with Instant Ocean. Different salts have differnt ingredients in increments of calcium/alkalinty etc... Wo ti really depends on how much money you want to spend and what you need the salt for.
I think the same goes for test kits. I used the cheap test kits for ammonia/nitrate/nitrate but use sailfert for ca
. I've found seachem are very good kits as well but think I will stick with Sailfert from now on.