Cross Platform – Being a Mac user I prefer when I can fire up a program locally. WordAi is web based and therefore works on Windows & Macs without issue (Linux as well). SpinnerChief III Ultimate has a Web Api that allows spinning from the web, but we did not have much luck with it, so at this time we consider SpinnerChief a Windows only application and therefore requires me to run it in a virtual Windows Machine using VMWare Fusion. This one is a hard one to call because clearly WordAi wins cross platform, but it doesn’t have all the extras that SpinnerChief offers.
If you have not used a spinner before then I would suggest that you first use something that require more human imput like The Best Spinner or Spinner Chief in order to understand the basic principles. However if you must go fully auto then I would suggest you go for Wicked Article Creator. I have it and understand it is similar to wordAI but a one off fee of $47.

There are some 'free' article spinners out there that require you to enter your text with properly formatted 'spintax' in order to create the end result. But how you need a totally separate tool to create this machine formatted text, so how is this really useful to you? Spinbot does all thinking for you, from taking in the context of every phrase to creating additional textual content that is as readable and meaningful as the text you originally entered.