They are right, upstairs is best. However, for your first trip in Upper, downstairs is a fun place to be and the bar is usually a good place to find interesting people to chat to (or boring ones to avoid). You will doubtless enjoy your trip. I still recall my first trip in UC from (thinks) October 1986 and the seats were just large 'Club' seats in those days. Then the introduction of personal video players and a library of tapes ... yes, those were the pioneer days.
Some years ago, SAA used the upper deck on theirs for Y and that was a real bargain.