The ease in which we can configure it, as well as our ability for customization once set up! It's not just about being able to accept credit card payments; there are so many other features available with this program including gift cards (which I am using now), employee rewards programs such as Amazon or Starbucks points etc...
We have been very happy thus far but if you're looking at any additional functionality please do your research because they may be missing something out from what was promised upon purchase/setup. As mentioned above - great customer service when issues arise during setup process / post implementation support has also always exceeded expectations.