Mullvad is much friendlier to privacy, but their proxies get blocked by A LOT of stuff, they also have a very small number of proxies. Mullvad collects literally nothing about you, but that's a double edged sword. not having any way to verify exactly who paid money into which account number means they can't help you if someone steals your account. I also have it on good authority that mullvad isn't very reliable at getting past more aggressive censorship firewalls. the one in china for example won't allow you to use mullvad unless the sim you're connecting from is a US one.

Proton doesn't record anything you're doing with their VPN and they've had to prove that many times and their "sentinel" program and the 2FA and double password you can enable make it very hard if not impossible for someone to mootch off your account. I very rarely get blocked by anything when I use proton VPN, if I ever do get blocked I just have to change the proxy I'm on. I don't even have to change the location most of the time because proton VPN has a huge number of proxies at each location.

Proton also gives you the ability to save recovery phrases and recovery files if you lose your password(s) or your 2FA

ente auth and ageis auth are great for storing your 2FAs and they allow you to back them up to a file if your account with ente fails in some way or if you forget the password to get into your ageis

as for those recovery files and phrases I talked about. save them in text files on a small capacity flash drive that you don't use for anything else