Physical vs on-screen
I've had phones with both over the years and my current handset, an HTC 10, has the middle ground of a navigation bar with touch sensitive buttons. Sometimes I prefer one over the other but if I don't hit a physical, touch sensitive button just right it might not register the key press. That really bothers me. Physical allows more screen to be used for everything else but can look ugly if done badly. On-screen can change to suit what you're viewing but in my experience it rarely, if ever, does.