What kind of time travel do you have in mind? Would there be different timelines or just one? If only one timeline, would Luke be able to change the past, like in Back To The Future, or would his actions ultimately lead to the events of the OT?

I think all of these concepts for time travel have their flaws, so I don't think any of them would have been adequate to use for official prequels. They would ultimately devalue the originals.

As for a fan-made story, any of them might work, if it doesn't take itself too seriously.