Lower body:
Squats in both ME and PH: ME squats are about 3 min long and use only traditional quats. PH squats are about 7 min long and use both traditional and plies. Imho, PH's squats are much more exhausting.
ME and PH both have lunge segments, PH's is longer and tougher imho.
The squat and lunge segments are the only lower body work in PH, ME contains 3 sets of leg presses, as well as a set of glute raises. If you do the lower body only premix on the ME/BC DVD, it's quite a nice, time efficient lower body workout.
Chest: PH uses a barbell, ME does not. The push ups in ME are a challenge, but I think the chest work in PH is tougher.
Back: ME contains a new move called the clean and press. I really like it. I think the back work in ME is tougher than PH. I think Cathe goes heavier for one-armed rows in ME than in PH, so you could go heavier in PH to make it more of a challenge.
Shoulders: PH's shoulder segment is so fun. I love it. Cathe does a variety of moves. In ME, she does a variety too and uses 5's and 8's. I use 8's and 10's and like the way this feels more. Overall, I think PH's delts' segment is tougher.
Biceps: ME is toughets, hands down. A 20# bb might sound light, but don't let that fool ya.
Triceps: PH triceps segment is a fryer, as Cathe would say. You do lying bb extensions, stand for kickbacks, then go back and do more extensions. ME's tricep segment is nice, just not as tough.
Abs: ME has my favorite Cathe ab segment of all time. PH's is a nice, short routine, but it isn't 'intense', whereas, I think ME's is.
Hope this helped!