If you are looking for free software go with Spinner Chief... If you are looking for paid software go with The Best Spinner...
I have been using The Best Spinner for awhile now and find it very easy to use. If you are careful how you "spin" each article, take your time doing it, the articles should come out okay. I use it for my own articles as well as provide an article spinning service using this software.
Content Boss is a good one. I'm currently using Automatic Article Submitter and you have to spin it manually but the software kind of assists you.
I don't like spinning but if I have to, the best for me is WordFlood - although not really automatic.
The best way is to spin the articles manually, then compare with some of the industry's article spinner, the Free article spinner is highly recommended, but before deciding see if it matches with the quality of your own spun articles
Dude... don't use spinning software. Think about it this way. Do you really think a multi-billion dollar company such as Google doesn't have an algorithm that can cross reference similar adjectives/verbs and then map that to the original article? They have that technology!
bestspinner is by far the best available there IMHO Spinner chief i havent tried yet, so no comments But remember that it is pretty much easier for any algo to find out synonym spun articles and i am sure these bots are capable enough to find them out until and unless you spin madly and that is the time your article looks like more of junk, so go the sentence level spinning way though that you need to do it manually, it gets your results and is worth the time.