In the original theatrical release which I saw as a little kid it was definitely "Luke, I am your father!". But there have been multiple releases since including the original version on VHS in the early to mid '90s, the digitally-edited version in the late 90's, and the revised digitally-edited version in the early '00's which is the current one. So there are multiple opportunities there for dialogue changes and in fact there was new dialogue added and some dialogue re-dubbed between these various versions.