Honestly they're both good, go with what you're comfortable with.
I use mullvad browser because it's Arkenfox plus tor plus ublock origin. It's just easier out of the box for me, especially because I hop between multiple computers.
If you're asking, means that you're willing to go through arkenfox configuration, setting up your rules and parameters, etc... So I'd say go for it. You can always go back to LibreWolf.