Here's an interesting dichotomy...

It is possible that it is only obvious to people who have seen the OT already, because Palpatine looks so much like the emperor. So this would support George's contention that you should see the PT first - so that you don't get the palpatine reveal.

But if you see the PT first, you get the "Vader is Luke's father" reveal. So you should see the OT first so it doesn't spoil the dramatic revelation.

In this respect, the PT spoils the OT, and the OT spoils the PT, so there is no suitable order to watch the entire saga. Best to avoid the PT altogether :)