Its really a hard call, there are so many factors that are involved from the number of trains on each line, line lengths etc etc.
I could really break it down and go into a huge amount of detail but the simplest thing to remember is the resort monorail does make a stop at the contemporary which will slow the trip down by about 2 - 3 minutes. Typically during a large exit at the end of the night there will be 3 - 4 trains on the express beam which usually causes a traffic hold just outside of the Polynesian while the train ahead moves out of TTC.
Typically during a exit the lines are much longer on the express side however they do move quicker. Sometimes Id day the express is quicker, sometimes the resort would be its just one of those deals where you have to see whats going on and how many trains are on each beam. At the end of the day the difference is probably very little for or against each side that its hardly even worth trying to figure out.