We did buy a trailer fairly early on, but he didn't like it. In retrospect, I shouldn't have been surprised. The trailer is much more like a car than like a bike: he's low to the ground, with limited visibility, and has to stare at daddy's rear wheels and legs. So we started shopping for a child seat. We ruled the rear carriers out of hand, because that was only a mild improvement over a trailer. I also wanted to be able to monitor Bowen, and a rear mounted seat doesn't work that well for that.
As far as front carriers are concerned, there are only 2 choices, the WeeRide, and the iBert.