Most of the game I have taken in PA have been either from the standing/offhand or sitting position. I have even taken a few using the opposite shoulder while sitting. On the other end of the spectrum almost all of the game I've taken out in the western states were from a prone position. So it is as you said. It depends on the terrain and the situation.
The most important thing to do is practice from all positions. I'd love to have all my shots taken from the prone or sitting positions but it just doesn't happen. Kneeling is good too but not on moving game. Then about the only position is offhand. And if you don't practice it you shouldn't take the shot. The animal deserves proper bullet placement.