OAR for me. Usually that means widescreen.
But not always.
The Truman Show
was intentionally filmed in an almost full frame ration of 1.66:1 because that's what the director wanted (he figured it was a TV show after all.)
When I watch Star Trek
episodes from the various shows using Netflix on the Wii on my widescreen TV I always use widescreen. I find the black bars on the sides very very annoying (yet I never mind the ones at the top for films) What I've found is that is that while technically the picture might be stretched, it's not noticeable enough and actually it looks great. that's the only exception to my OAR rule.