Just some thoughts:
- consider what you'll want for day to day use as well as other tours
- panniers can be customized for a specific purpose [ie. 4 panniers for big trip, 2 lrg rear panniers only for moderate trip, 2 sm front panniers only, down to a single pannier]
- the shorter bike with panniers is easier to maneuver and get on/off transit connections
- trailers are nice because they get a lot of the weight off the bike and you can quickly turn your bike from cargo/gear hauler to light day to day ride
- being able to fly your Bike Friday for free [check with your airline] could be a benefit that pays for the trailer
I don't think there is a wrong answer here...both solutions work...depends which issues you care about more?