I've used Instant Ocean, Oceanic, Crystal seas bioassay, and now Reef Crystals.
IO - Very inconsistent over the last five years. Low in Alk, Calcium, Magnesium, and mix PH varies between buckets. In general, IO varies too much for my taste.
Oceanic - I saw a Diatom problem when I started its use (do a search on ReefCentral as others have had the same problem). After I stopped using it, the diatom problem went away...
Crystal seas - I really liked this, but it was expensive
Reef Crystals - Mixes faster and more completely than IO and has better Alk. Still low in Calcium and Magnesium, but so far the aquarium inhabitants seem to like it.