It sit with my feet on the toes: the left foot is mostly handing off the edge of the foot stool and my right is back and on its toe. (see my seating position here.) This is not uncommon: a lot of methods advocate it, and a lot of professional players sit this way.
Now contrast that with how David Russell sits. Feet flat on the footstool and the floor. It looks more comfortable and stable.
What do you do with your feet? Do you feel one method has an advantage over the other? If you use a guitar support, please weigh in with your thoughts.