This is really case dependent. You cant completely rely on the software for all articles, They might work well on some while on other you will get a good reason to laugh. Either get them rewritten at a cost or atleast proofread the outputs of various softwares, best of all being The Best Spinner
I am using "The best spinner" for spin article. But I think after spinning the article even we can not get rid from duplicate content. Ezine never accept the spinning article.
then the problem lies with you - you can make it as different as you want with modern spinners. Such as spinrobot. for example.
If you want 1 for free, try freetrafficsystem. I cannot seems to get it working but I heard lots of people are benefit from these.
that's just a jetspinner - you have to hand-create the {cat|moggie|pussy} syntax. There are loads of free ones out there that don't require you to sign up, if that's all you want to do (produce versions from a prepared syntax text).
The spinner I use is easyarticlespinner.net it keeps on innovating. This is so much helpful because I need multiple submissions of my articles.