Anonymous transactions with bitcoin core
Your VPN provider at least is in a position to deanonymize you. Therefore, I would rather use TOR. It's not infallible, but many people have used it successfully to achieve relative anonymity. Here's a short guide to setting up bitcoin core with TOR

As Saxtheowl has already mentioned, however, both a VPN and TOR can only hide your IP address. There are many other ways to get deanonymized. Fortunately, there is a comprehensive guide about everything you need to know about using Bitcoin in private