You should use Biometric security to protect your phone so that no one can access it but only yourself
Password is safer as DaveF commented, if only password is used, can the wallet also be accessed if the password is unknown, it will be difficult. Also what if you are sleeping and someone that is close to you make use of your finger to be unlocking your phone, apps including your wallet to compromise it. Biometry can be good for easy access, but not as secure as passwords.
Do not even have to be sleeping. If you are out drinking or whatever, and (being sexist here deal with it) those attractive women at the end of the bar come over to talk to you it's going to be easier for them to get you to unlock your phone so they can 'put their info into it' or to get you to take a picture then it is to have you enter the password 87g7w458w%Y$W!(SERGdvf
Also, on that note. I am surprised that more apps don't have geo fencing on them. Yes you can unlock you wallet with a fingerprint. But you have to be at home to do it kind o thing. There is at least 1 BMS app that I know of that you can only connect to the controller if you are in the area. Surprised more apps / things don't do that. Or if they do exist I have not seen them.
-Dave