I was watching Return of the Jedi yesterday, and was rather struck by the scene where Luke is presented to Vader near the landing platform. In that, Luke really seems to put psycological pressure on Vader, and is winning the battle. What he says about his father, hoe he feels good in him, and says he couldn't be turned, affects Vader tremendoulsy. Vader responds by (1)denying it, "there is conflict," (2) changing the subject "I see you have constructed a new lightsaber," (3) giving up, "there is no hope for me," and (4) changing the subject "the emperor is your master now." and then at the end of the scene, he kind of sighs and looks out the window contemplating.
I think Luke clearly had the upper hand in that "battle" and that was the most intriguing "battle" of the film.