The top one (purple box, less expensive) is "regular" instant ocean (IO). The orange box is IO reef crystals (IORC). I use both, depending on just where my parameters are at the time.
Starting out with a newish tank and few if any corals, IO will be more than enough. Down the road, if you get a heavy coral load (LPS/SPS) and start using more calcium and alkalinity, then you might switch to IORC.