Aiditorial Article Rewriter is the best article rewriter tool. Aiditorial Article Rewriter provides alot of options to customize the software.
Many of the features are the same but the thesauri are a little different. SpinChimp will be getting phased out once ChimpRewriter goes live though (2015), so you shouldn't be installing it.
ChimpRewriter - Best Article Rewriter - helps rewrite your article in seconds. ChimpRewriter Article Rewriter checks for duplicate after you rewrite.