Neither.
Instant Oceans isn't as high in trace elements as it should be for a reef tank. That's why aquarium systems started marketing another brand reef crystals, that's higher in the trace elements that are useful in reef systems. The rep that we had at one of the club meetings awhile back basically said that they were recommending the IO for FO tanks and the RC for reef tanks.
http://www.aquariumsystems.com/frames1.htm
Some people seem to get very good results with oceanic salt, but from reading hundreds of posts about people having huge algae, and diatom blooms after switching to oceanic, then only managing to get rid of the problem by using another brand of salt I'm pretty convinced that they've got a problem with the consistency of their mix. I won't be using it.
I use crystal seas bioassay salt. It's really not available here in town so I'm considering switching over to Tropic Marine pro when I run out. I've heard lots of really good reviews about this salt from people that I respect, including a coral farming company here in town.
B