I do mine upside down for the simple reason that it is easier, altho backwards but then I am a closet lefty so..... I don't worry about bumping things too much since my bike is light enough for me to swing out and turn over without bumping the garmin and computer which are on the aero bars and are protected by the bend in the aero bars. When it is upside down it rests on the tips of the aero bars and the seat.
I have a hard time remembering to take the stuff out of the seat bag before flipping it though, Fortunately, the whole bag comes off easily upside down. 
marni
marni
Katy, Texas
Trek Madone 6.5- "Red"
Trek Pilot 5.2- " Bebe"
"easily outrun by a chihuahua."