Buttons all the way. The apps aren't all built for the screen, and forcing them to use "full screen" frequently causes issues, so...why not a navigation bar? Besides, it can come and go as needed.
Plus, I can use Good Lock Navstar to create my own nav bar--including an icon for quick tap for screen off, the same thing as pressing the power button, except it's WAY more accessible on S10+ than that stupid position for the power button. (S9+ power button position was WAY better and easier to access.)
Buttons all the way. MUCH more productive.