If we're talking about any version of Superman, then I believe the Pre-Crisis Superman (yeah the one that existed in DC Comics from the mid 1950's to the mid 1980's) would be quite a formidable opponent for 'ol Skywalker.
Why? Well considering the guy could literally blow out a star with his 'super-breath', and was shown to be able to juggle entire planets like apples, confidence in the guy kinda goes up after feats such as that. Also, Pre-Crisis Supes wasnt limited to one Universe as there were indeed numerous stories involving him traveling to other universes with alternate earths (Earth-2, Earth-3, Earth-Prime ect ect) for various reasons.
So ultimately, Luke vs. Post-Crisis Superman ... I'll go with Luke on that one.
But if it's the Pre-Crisis Superman (Golden Age Superman as well since he was shown knocking out the Pre-Crisis Superman in COIE), then I gotta go with Supes.
Why? Well considering the guy could literally blow out a star with his 'super-breath', and was shown to be able to juggle entire planets like apples, confidence in the guy kinda goes up after feats such as that. Also, Pre-Crisis Supes wasnt limited to one Universe as there were indeed numerous stories involving him traveling to other universes with alternate earths (Earth-2, Earth-3, Earth-Prime ect ect) for various reasons.
So ultimately, Luke vs. Post-Crisis Superman ... I'll go with Luke on that one.
But if it's the Pre-Crisis Superman (Golden Age Superman as well since he was shown knocking out the Pre-Crisis Superman in COIE), then I gotta go with Supes.