DevComp

Here's why you should never use free VPNs, this is highly accepted cybersecurity advice.

I would personally recommend Mullvad, for the reasons I will list below.

Mullvad actually runs their servers entirely in memory, so the moment a particular server is disconnected from power -- there is practically no data that is retrievable.

On top of that, Mullvad collects zero information about connections that can link them to you. When you sign up, you do not provide them with personal details like an E-Mail address, but are rather given an account ID which is your only way of accessing your account. Payments with purely anonymous crypto and cash are recommended (I believe they give you a 10% discount for crypto payments to encourage them). In case the server provider were logging request data, it would still be hard to associate them to users due to this system.

As others have already mentioned, they also implement a lot of privacy and security features into their client itself, which not many other providers implement. Mullvad has been an early adopter of Wireguard and has been investing into VPN tech for a while too, if that helps.