The "correct" (by which I assume you mean "Standard English") for this would be to say:
It was the best restaurant I have ever been to.
It was the best restaurant I ever went to.
Note that ungrammatical text is quite common in some dialects, and can often creep in when people speak quickly or with an incomplete grasp of English (for example people learning English as a second language, or children).
As a learner you should try to focus on speaking Standard English yourself (unless you have a good reason not to), but be aware that other people, including native speakers, won't always speak perfectly grammatical English back to you.