Everyone I met using a trailer either loved it or hated it. Everyone I met using front panniers loved it and some asked what a trailer would be like. Therefore front rack > trailer.

For a more thoughtful insight I can say that I traveled with a couple people who pulled trailers and they were always a huge pain. Tires would go flat and eventually wear out. Sometimes the frame of the trailer would break. Try finding spare parts in South America. Not easy. To me a trailer is just something more you have to worry about but if you're staying in Canada or the States it shouldn't be a huge problem. Trailers may not cause any problems but IMO they are more of a hassle than having a nice compact ride.