I have tried (or at least seen demos, but that's only for conversion.ai, the others in the list I did try):
- rytr.me
- conversion.ai
- writesonic
- synthesis (you need to be a member of prosperative.com to access it)
- articleforge
- snazzy
... and many more (honestly) that I can't even remember their name. And what I can tell you is this:
ALL of them are equally good or equally bad (depending on your view). They are equally good because they can help people who hate writing (like myself) to build content without breaking the bank.
And they are equally bad because no matter which AI writer you use you will end up spending 10-20 minutes (if you are good english speaker), or hours (if you're not good english speaker) proofreading the content, fact-checking it, fix the grammar errors, and - generally - edit it to convey the right idea just the way you want it and to make sense.
Over time these content writers have been improved a good deal, but they're still AI writers at the end of the day, and if you don't take the time to review and edit the content they produce anyone who knows a bit of english will be able to tell that the content has been generated by AI, or by a really unknowledgeable english speaker.
Of all the content writers I have tried I like rytr.me the most. Is it the best? I don't know. But it's what I prefer