You are right, we only use Kosher in our kitchen,and it contains no additives. However, it's more expensive than regular old iodized, and so the price difference between Kosher and Aquarium salt seems to shrink.
I recently had a GT come down with ich due to stupid wet driftwood from my stupid LFS who feels it necessary to keep their driftwood in their stupid pond. LOL anyway I chose to go with Aquarium salt simply because if I used up all of the Kosher, I'd have to buy more of that, anyway, and it's really not that much cheaper than the stuff at the LFS.