This article try to run live test and compare accuracy of several popular plagiarism checker https://covenantlinks.com/blog/which-one-is-the-most-accurate-plagiarism-checker-we-will-test-some-of-them/ You can decide yourself then. Hope it helps
It doesn't really matter if your content is unique or not, what matters is how Google treats it. If Google doesn't find it, it means your content is unique. That's why I always check only Google.
I think Grammarly is the best tool to check plagiarism reports, it is not free but it gives an accurate report. You can also try smallseotools or duplichecker tool, both are popular nowadays.