Question: Barbell Rows or Single arm Dumbbell Rows to work the lats & upper back muscles over a full range of motion?
Probably single, alternate arm dumbbell rows.
You should be able to get better tension and range of motion from this exercise. But try it unsupported, not leaning on a bench, bracing your non-working arm against your thigh in a kind of crouched over, lunge position for a better functional effect.
These photos aren’t brilliant, but will give you a general idea of what I’m talking about.
The issue with BB Rows is that most trainers overload the bar. They also tend to sacrifice form, jerking the weight off the ground, putting the lower back under risky stress vectors and in jeopardy, while getting relatively little muscular payoff for it.
While the dynamics of the Alt. DB Row tend to make you play it a little more honest. Do exercises need to be honest to work better? Perhaps the answer is “no, not always.”
But in the case of this one, it is the best policy.