Ease of use provides almost the opposite ordering. The arms of the Portland racks were difficult to get into the correct position, especially on bikes with front fenders, which provided little clearance between the front wheel and the downtube. There were also subtle adjustments available to the shape of the jaw which we did not notice at first, and which most bus riders are not going to have the time to examine and decipher. Considering how many bicyclist do not know how to operate their quick release tires properly, we regarded it as unlikely that everybody would figure out how to adjust and close the more complex Portland jaws correctly. The arms of the Sportsworks racks were probably the easiest to use, but none of us were willing to trust our bikes to them.
Ease of use consists of more than just figuring out the arm mechanism.
The Portland rack uses Yakima extruded trays to hold the wheels, rather than the wide wheel wells of the Sportsworks and Phoenix racks. The arms on all the racks have to be held in a folded-down position when the rack is not holding a bicycle. The Phoenix latches also were not self-closing, and would swing against the bus when the rack was folded up unless the driver got out to fix the problem. I don't remember any problems with the latches on the Portland racks. We felt that both the Sportswork and the Phoenix designs could be improved by using either a cabinet-style magnetic latch or a large area of Velcro on the side of the arm.