I was using Instant Ocean but now I'm trying Oceanic, which doesn't seem to be on either poll. Not sure if there's much of a difference, really, except for the calcium content.
I used to use IO, but have recently moved to Reef Crystals because the trace levels are closer to what I am looking for.
I didn't use IO because it was cheap, I used it because I could always get it when I needed it. Too many other salts aren't stocked regularly locally, and I think it is consistency is critical to a healthy reef.