As an expert writer and researcher, here are the five plagiarism checkers that I would recommend based on their popularity, effectiveness, and features:

As an expert writer and researcher, here are the five plagiarism checkers that I would recommend based on their popularity, effectiveness, and features:

1. Turnitin: Turnitin is one of the most widely used plagiarism checkers by students, teachers, and researchers. It offers a comprehensive plagiarism detection service that checks for similarity in submitted documents. It does this against a vast database of academic papers, websites, and other sources.
2. Grammarly also known as a writing assistant that checks grammar, spelling, and punctuation. However, it also includes a plagiarism checker that compares your text against billions of web pages and academic papers.
3. PlagScan: PlagScan is a powerful online plagiarism checker that scans documents for similarities against an extensive database of academic and web sources. It offers a range of customization options, including exclusion of certain sources and citation styles.
4. Copyscape: A lot of people use this plagiarism checker that helps website owners check for duplicate content on their website. It offers both free and premium plans with features such as batch search. Also, it has API access, and private index for users to store their content.
5. Quetext: Quetext is a popular plagiarism checker that offers a free version with limited features and a premium version with more advanced features such as deep search technology, citation detection, and integration with Google Docs. It also offers a downloadable desktop application.

It’s important to note that no plagiarism checker is 100% accurate. Notably, it’s always advisable to review the results manually to ensure that they are valid.