IO and Reef Crystals are all that I have ever used. Both are reasonably priced and very available (latter is key as I am pretty religious about water changes and would be uncomfortable switching salts cold turkey). They are basically the same salt except that RC mixes to a higher Alk and Ca - purportedly designed for an SPS reef. RC does mix with pretty high Alk and Ca - which is where I run my reef - so I can just mix and go. With IO, I have to add 2 part before I introduce to system so as not lower my Alk/Ca. Many, many, many TOTM both here and on other sites have used IO/RC, but I am following your thread as well to see if I am missing out.