What is the best online plagiarism tool

Does anyone know about a specific online plagiarism tool, as we have searched and used many by search online in google and also tried many of them but dont know why after checking few copies it always give plagiarism error no matter my content is 100% unique, i m fed up with this, can anyone help on this regard?

Some of the schools in my area seem to favor this one: http://turnitin.com/

Although it’s probably geared more for academic papers, than website content.

there are several threads in this forum about online plagiarism tools. Please use the search feature and read through the threads. Then if you have a question about a specific tool, feel free to begin a new thread and ask it.