Check out this thread. This does a comparison between the 7.3, 6.0, V10 3v, and V10 4v.
Longevity Test-5 PSD's vs V10's - Ford Truck Enthusiasts Forums
Kind of a long read but interesting.
7.3 all the way!! Although from what ive read, both the 5.4 and 6.8 are great motors.