rotj luke would probably win in a saber duel, ben hasnt dueled or sparred since he came to tatooine, being seen with a saber would be enough to cost him his life and possibly give up lukes position. in anh i think the only reason he brought it out was because he and luke were leaving and he knew the imperials wouldnt be able to track them.
force duel im not sure. luke is supposed to have the potential anakin would have had he not been confined to the suit. so although he wouldnt have achieved it he was still very powerful. plus he used some dark side attacks obi wan wouldnt have. 50/50 i think.
last one i think luke would win. he never seemed to be in too much danger when he was fighting vader in rotj, and in the end drove vader back and bullied him to the ground before disrming him. luke 80% of the time.