Since the OP is an apartment dweller, as I am, he may want to consider parking and storage issues as well.
I'm leaning towards a trailer, myself. I could never get an Xtra into my apartment. A regular bike is long enough to leave tire marks on the walls in the 180° turn on the stairwell, and once inside, I'm not sure I could reach the brakes to do the "tip it up on its back wheel to steer it around the furniture" trick.
Meanwhile, I could stash a trailer in the basement, (which has a ramp, but a 90° turn to get in the door, again a potential problem with the length of the Xtra) or even chain it to the fire escape. There's less to rust on a trailer left outside than there is on a bike. Lower theft factor too.
They each have their advantages, and ideally, I'd like one of each. But given the architectural limitations of apartment living, the trailer is probably the better bet for me.