I voted for release order because the scene (why am I using a spoiler when everyone should know the originals!) Spoiler:
where Darth Vader tells Luke that he is Luke's father is not as powerful if you already know that Vader is/was Anakin. Everyone knew it was coming but it just is not as cool when you are absolutely sure! That is a reason, but, mainly, I would keep Lucas's vision of the Star Wars saga in tact and leave them in release order. He had reasons for starting there, and I forget as of right now but I am sure there were reasons.
$0.02