IO and IORC are often the same price on Amazon (yay prime! Those boxes are heavy lol).
I don't think it makes much diff which you use. I been getting the IORC lately and it's fine. It's ready to use after 20 min mixing in cold water and fairly stable params. Sometimes it will precipitate if it gets warm, but any salt will if the alk/mg/ca is high. IO won't. Also, I heard rc has some organics that can make the bucket grungy, but I haven't noticed anything myself.
I'd be shocked if you noticed any diff at all between brands in a new tank without a heavy hard coral load, except maybe your wallet being lighter and your heaters getting crusty if you go fancy. I do think that if you are trying diff brands it's a good idea to mix the old one with the new one for a few water changes. So like if you want to try a spendy salt don't wait till you're all out of the old one. That'll be a gentler transition for the tank.