My Advice to Anyone That Has Not Seen Any of These: Start with 4, 5 and 6
Before recently, I had never seen any other Star Wars movies other than the original three.
I would strongly suggest one watch the original three first because if you start at the "new" ones, the impact of what goes on in 4,5 and 6 won't be as resonating.
I know it sounds weird, but if you watch them in the "new" order, the later big surprises won't be big surprises....