I traditionally used IO and RC. Now I use Seachem Reef Salt ($35 a bucket through club powerbuy...can't beat that), I think it mixes at lot more 'clean' than RC. I think if you're already supplementing your sps tank and you're doing regular water changes, then the salt mix isn't that critical.
You'll see plenty of very successful large sps tanks that use IO...
TMPR or Red Sea.
I've heard really good things about seachem's salt from others.
D&D by far the best consistent salt I've used.