Mullvad's policies and account creation process demonstrate an awareness and commitment to privacy as a number one priority. Yes, at the end of the day, none of us really knows what a VPN service is doing on the back end, but the fact that they have detailed public information about their operations, as well as additional privacy options such as paying with cash/crypto, is a good sign. Other little things, such as supporting WireGuard and running their own Bitcoin nodes instead of relying on third party services for crypto payments, are also good signs that their team has above average technical chops compared to other providers.
[1] https://medium.com/@derek./how-is-nordvpn-unblocking-disney-...