Interesting topic Greg. But I have to disagree.. I'd go with 123456... Mainly because they wont be disappointed with the suckyness of the first three episodes. Then, when they get to the original three, they'll end it on a high note.
Plus, kids might enjoy (I know.. it's a stretch) Jar Jar Binks and his crazy, wacky hijinks... How do I express sarcasm on this?
Might want to start them with the Christmas Special so you can set the bar really low right at the beginning... It doesn't get worse than when Bee Arthur sings and dances to Alien Klezmer music!