Reef Crystals for 8 months, I.O. for 10 years. I switched because i struggled to keep my alk and cal high enough. Have been really impressed with how the cyrstals are working out.
I use Kent Reef Salt, it's cheaper than IO, however I know many people who use IO in a reef tank and it works just fine. I have been using Kent for 3 years in my mixed reef, been very happy with it, and it is what I can afford.
i have been using salinity and really like it, the only issues are that it is a bit spendy and you have to let it mix for a while or it will leave a haze on your glass.