I prefer downstairs. I'm a bit claustrophobic and the low ceiling and small space (2-2 seating) make it feel like a narrow body up there. I prefer looking upon the spaciousness of a wide body on a long haul flight. And has been mentioned, really small overhead bins up there, and service downstairs always seems to be better. I always walk downstairs and they seem to get continual service. Upstairs is definitly the sleeping compartment, but since I NEVER sleep on a plane, downstairs is the place for me.
How many of you can remember the Piano Bar upstairs on Pan Am's LAX-JFK Transcontinental Service (I think I recall TWA having it too). Those were fun days to travel. When I think of all of us drunks up there singing around the piano...and the smoke!! Yech! How did we ever stand it?