If you lead the thing to the pipe, the flange often does not have any screw holes to anchor it to the floor (some do). A plastic (or metal) compression flange, either glued or sealed to the waste line needs to be screwed down to the floor as the pipe is not strong enough. Ideally, the flange is set on TOP of the finished floor with the bottom of it flush and level on the floor for any type you use. My unprofessional opinion. Either will work and last if the subfloor is installed properly, the flange is anchored to it, and your wax seal doesn't leak and rot the floor.