You have a lot of options for training the rear deltoids, the exercises are all similar to one another, I have experimented with different movements for years in my programs, and I cannot say there is any one movement that is supreme.
Because the posterior deltoid’s are predominantly type one slow twitch muscle fiber, I think they are best trained with high reps, they are already being recruited on your heavy Rows and pulling motions, but to be targeted directly high reps work well.
The weights do not need to be particularly heavy, this is a situation where you do want to go for the pump and burn, add lots of reps before you ever add weight.
I do not think they need that many sets to be trained, one or two sets in the 15 to 30+ rep range is more than enough. Maybe 3 if you’re feeling ambitious.
