What chat box or plug ins do you use on a website? The one that easy to implement?

This is a tough one. It depends a lot on the platform the website is built on and its purpose. For e-commerce a paid chat plugin is preferred like Olark or LiveChat. For a wordpress site there are free solutions that are pretty nice for simple chats like tawk.to.

If you can elaborate on what your situation is, then you might get more useful recommendations in this area.