you can't go wrong with IO. so many tanks for so many years have been golden on it. though it does have low magnesium, which i'm trying to stay on top of these days and since it's so expensive to boost Mg i'm thinking of switching, either to kent (lots of big names say good things about it), oceanic (ran it before and loved it at first but then had a weird algae that i blamed on it at the time but was probably unrelated), or maybe even try the seachem reef salt since i really like seachem products in general. there's an asian import salt called oceanpure or something like that, that is becoming really popular on the west coast where it's available. works good and is really cheap if i've heard things correctly. i was interested in trying tropic marin for a while, but after seeing the latest salt study, i don't really see how it's much different from IO other than being alot more expensive.
the only salts i would *never* use are crystal sea, coralife, and red sea.