i really dont think there is a best salt. i use Kent Marine salt myself. why because when i used IO i always had calcium issuses, when i went back to Kent the calc issues went away. and my water was clearer. but thats just me. many people are successful with many brands of salt. i recommend getting one thats available to you locally, and works for you. its fine to by the same brand online, but make sure you can pick up some quick for an emergancy!
.