Each is different, so it's best to check out what each offers and which best suits your need. In many ways, a new one, (rather unimaginatively) called Store, is really good, so worth considering. There are some nice membership addons, too, depending on what you want to do with membership. You can search all the addons at the Devot:ee site.
iii, EE doesn't have many eCommerce add-ons but they're all good in their own right. I'd read up on each of the ones mentioned in this thread and see which one comes closest to your requirements. They're all good, however, as are most EE add-ons.