I did both of these last week. I think they are both very useful and I wouldn't eschew one for the other. PP 3x's is tougher than the SS 2x's (PP is 65 min. and SS is 59 min) because with SS you break up the shoulder work and with PP you do it fairly close together (and PP's shoulder work really fatigues the triceps, imho).
Supersets 2x's upper body premix is one of my favorites. I really feel challenged with this one - partially because it has many new exercises (like preacher curls on the ball) and partially because the sequencing is different. Push Pull 3x's really works the muscles too, but you do less variety as far as the moves are concerned.
But like I said, I do like both of these workouts.