I think the best way to watch it is
1,4,5,2,3,6,7
1 you get to know Anakin Skywalker, the slave/person/pilot/etc. Then it skips to Luke, hiding the reveal of Anakin becoming dark in 2, and the Vader turn in 3. You also remember how good of a pilot Anakin was, when Obi-wan is talking about him to Luke. You find out who Vader is in 5, so you go back to Episodes 2 and 3 to watch how Anakin became Vader, to finish the saga you RETURN to see 6 and go right into 7.
or
You can just watch 4,5,6, then 1,2,3, and finally 7.