I prefer the OAS. If the film was originally created in WS then I prefer WS over 4x3. If the film(or tv show) was originally 4x3 then I prefer that over WS.
Also, using Full Frame in this context doesn't really make sense. Full Frame refers to filling the whole screen. If you have a 16x9 screen then Full Frame implies a 16x9 imagine. If you have a 4x3 screen then Full Frame implies 4x3.