0:everything-but-the-last-slice is the ratio that works out best for me.
Pizza should be consumed only with root beer, ideally in a restaurant with wood laminate tables, ancient odorless red pepper shakers relfecting the multicolored light of low-hanging stained glass lamps. Background music provided by a constantly-swinging kitchen door and the cacophony of the pizza making processes within, in concert with an old Galaga or Turbo Ms. Pacman machine humming and blooping in the background.