I hope you meant plagiarism detection* site. :)
Turnitin is definitely the most popular. Helps with citations. Is widely used in the academic/research community - one of the groups most concerned about plagiarism.
There are many websites that offer free plagiarism checkers. The best site is one that will tell you if your work is plagiarized or not, so you can be sure that you are not committing any plagiarism. You should also make sure that the site does not have any hidden fees. I highly recommend you to visit https://lettersaboutliterature.org/ website where you can find the best plagiarism detector with percentage in this way you can make your content extremely unique and easy to understand.