There isn't a "one best", as far as exercises for back are concerned. There are just too many muscle groupings in the Back for only one lift to be considered the most effective. That being said, if I were in prison and had 30 minutes to get a rotuine in that day, I'd do Deads, assuming I could only get in that one lift, hypothetically(knock on wood). Reason being, is because Deads target the most muscles in the Back area of any other exercise. That does not mean it effectively targets them all though. Again, to get a decent back workout while doing extreme-minimal exercises, you would still need to add another lift to hit the lats more directly in my opinion, to top off the back routine. Pulls to the front, or reverse-grip pulls would be my choice, assuming I could only add that one additional exercise to the rotuine. Even though Deads RULE for Back, they don't target the lats as much as pulldowns(or other lifts) would. They are mainly a spinal erector lift, as far as the Back is concerned. Traps are included of course, as well as lower back in the erector category. Assuming by "middle-back" you meant the muscles running verically from Neck to Ass, then Deads are what you want to focus on brother. Hope that helped.