In my gym there´s an excellent rowing machine with vertical handles of shoulder width grip, that´s my favourite, I really feel my whole back´s contracting like hell on that.
I prefer barbell rows instead of dumbbell rows, because dumbbell rows give me little more than pain/strain in the shoulder girdle. I also feel my back is contracting better with BB´s than with DB´s, maybe because it feels more strict with BB´s. Besides, with DB´s you have to spend more time, since you work each side separately, and I want to keep my workouts as short as possible, to minimize the cortisol effects.
But of course, we are all different...