Powerlifters use a greater lower back arc, bring the bar down in a straight line toward the lower portion of the chest and keep the elbows relatively close to the body. All of which increase the amount of weight you can lift by making the lift mechanically easier.
Bodybuilders normally use a bit wider grip, keep their lower back tight, but not arched too much, bring the bar to mid pec and press it up toward the j-hooks. All of these make the movement mechanically more difficult so the muscles must work harder.
I personally prefer the power bench.
Well, DB flyes flat out suck. They only provide resistance during the first part of the movement. Push-ups are not that good either, unless you are very weak. If you can perform more than 12 push-ups, you are wasting your time with that exercise.
The exercises I favor are:
Base movements (most important): decline bench press, bench press, incline bench press, dips
Secondary movements: DB decline press, DB bench press, DB incline press
Assistance movements (least effective): CABLE flyes, CABLE incline flyes, CABLE cross-over