Good question. There are three that I typically recommend to people. Visual Form Builder and Ninja Forms are both good, easy to use plugins that let you create a contact form. And they are free with some paid extensions if you need more functionality.
I’ve been a Gravity Forms user for years now. While it’s not a free plugin, it really is an excellent choice.
Some people like Contact Form 7. It certainly is functional, it’s just not as simple to work with as the others (in my opinion).