salt is salt.
the rest is just marketing and minor elemental differences easily adjusted.

I use Seachem Reefsalt.
I dont habve to adjust alk or magnesium and it mixes clear within a few hours with no scum on top or unidentifieable objects found.
The price point is also great.

Some one in RC measures major elements in many brands of salt. here is the link:
http://reefcentral.com/forums/showthread.php?t=1714505

I have been using IO for years because it's widely available in our area (no fear of OOS), and it's the cheapest even with additional elements added (IO is low on Ca).

I'm happy with my Reef Crystals other than the nasty crap that builds up in my mixing tank.

Why use a more expensive salt that gives you crap like that?

My experience is about the same as this. I used high end for quite a while, switched to Instant Ocean, then tried a couple of other brands. I'll be sticking with Instant Ocean as none of the other brands seemed to perform any better, Instant Ocean is cheap, and I had to use less additives with Instant Ocean than some of the more expensive brands.

I've just always used RC. Maybe I'm a bit superstitious but I'm hesitant to switch. RC is also nice and high in Ca.

I use IO Reef Crystal. I tried red sea and H2O but my zoanthids were not doing well at all and I almost lost them all. I switched back to IO and they all came back to good health.

I used H2O for about a year and always had some brown deposite in the mixing baril. Never had this with IO or IO Reef Crystal. I will stay with IO Reef Crystal as this give me the best results. I have SPS, soft and LPS and all my corals are doing great.

NO matter what salt I was using, I always had to dose, so why buy a very expensive salt like H2O if I still need to dose about the same? no point. I am very happy with IO RC.

I use the BRS 2 part dosing and just got their pumps as well.