I find both of them equally (un)reliable. I feel like they both work(ed) about 80% of the time.

The most annoying failure case for FaceID for me is using it in bed. I'm a side sleeper so half of my face is mushed into the pillow. I realize how lazy this sounds, but when I'm half asleep... that is exactly when I don't feel like tapping out a PIN or repositioning my head.

    A fingerprint reader inside the powerbutton 
    is the way to go IMO

I really wish the phone had both methods, TBH.

I love the "reader inside the powerbutton" idea, but... phone cases....