Hi,
If you need to flip in bulk, using a spinner tool is the fastest. They may pass copyscape, but the text will very likely not flow naturally.
Otherwise, the best way is still to hire a writer, or write them yourself.
I wouldn't bother hiring a cheap writer (less than $5 for 1000 words) as they would most likely deliver poor quality writing, or use a spinning tool anyway then deliver the work to you.