Low transaction fees aren't important if the software and service aren't a good fit for your business. If you need to accept and track cash as well as credit card payments, for instance, GoPayment won't work for you. If you need to print paper receipts from iOS devices, you should consider PayAnywhere or Square. GoPayment is the best option for printing receipts from Android devices, and if you want the ability to charge cards via a Web interface in addition to using a mobile device. If you need a synchronized database for your inventory, or if you like the idea of scanning bar codes, SAIL is a good choice.
For more information, see our in-depth reviews of the four systems:
Eric Geier is a freelance tech writer. He's also the founder of NoWiresSecurity, which provides a cloud-based Wi-Fi security service for businesses, and On Spot Techs, which provides on-site computer services.