It's OAR for me, all the way. I know someone who has his TV set up so that everything except 4:3 (which gets stretched to 16:9) gets letterboxed. 16:9 broadcasts letterboxed on a 16:9 screen. And the naturally letterboxed movie ratios get letterboxed even more
until they're so vertically squished everyone looks like a frog.
Apologies for overuse of the word "letterboxed".