I have 3000 mi experience with the trailer and 20000 mi experience with panniers.
I don't like the trailer at all. I never got used to it. I feel a dead weight behind me which lives its own life. Of course the trailer stays on track and doesn't jump around, however I don't like the "inertia" in the system. To me, panniers become part of the entire rig and just act as one single heavy bike with no "inertia" problems (I don't feel the weight of the panniers counteracting my movements).
PS: I never had a problem with manouvring the trailer. It was never an issue for me - so this was the least "problem" to me :-).