ItemChoice doesn't show up on either Curse or WowInterface, but as I remember, it simply shows you the best piece of gear that is available as a quest reward. Neither that nor /equip does anything like what the Zygor auto-gear functionality provides. Auto-gear is a sort-of in-game function that looks at all your gear and selects the best gear in your bags slot-by-slot and if it's not already equipped offers to equip it for you. It's not perfect - for some classes and specs it is downright horrid - but for some it is terrific while you're leveling.