Recently did IAD-MSY-IAD with 6mo twins. Preboarded in my last month as a United 1K. Honestly, in the time it took us to break down the stroller, bag it and the car seat at the end of the jetway, half the plane had already boarded. If we had to board last, I think everybody on the plane would have been waiting for us to juggle everything. Oh, well -- next time, we'll at least have had more practice!