Vader’s actual quote has tons of impact because Luke had just said with great passion “He (Obi Wan) told me you killed my father!” (Although I am sure I misremembered the exact words.)
In any event, “Luke, I am your father” would not have been as strong. as “No, I am your father!”
Two lines that immediately come to mind, and I’m sure you can name the films:
“Jim, he’s dead”
“Yes, I’m serious...and don’t call me Shirley”
I missed that whole part of the the movie! I had our baby at the movies with me, and he started fussing, so I took him out so as not to disturb the other patrons. My sister and her kids came out of the theater all a-twitter and spilled the beans!