By now, most people in the SEO industry are more than familiar with the various animal named updates that have made it nearly impossible to rank without high-quality content. One of the most famous ones is Google Panda, which directly targets on-site content quality and severely penalizes sites that have spelling and stylistic errors or were not edited well.
There is also the option to spin capitalized words (assumed to be proper nouns) as well as leave any number of words unchanged, depending on whatever you enter into the "ignore" field, separated by commas. You also have the option to only keep the sentences that were altered a minimum percentage, as indicated by the "Keep Sentences that Changed" option.
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.
And then there is the amount of time that it takes to create content with this software. I have had past experience with text spinners and although it might seem like a fast way to write content, it often isn’t! By the time you have chosen a piece of content (or multiple pieces of content to blend together), put it in the software and produced content with this software, you could instead have created content that Google loves.