What is the healthiest way to sit?

What is the healthiest way to sit?
Best sitting position

keeping the feet flat or resting them on the floor or a footrest.
avoiding crossing the knees or ankles.
maintaining a small gap between the back of the knees and the chair.
positioning the knees at the same height or slightly lower than the hips.
placing the ankles in front of the knees.

Best sitting position
  1. keeping the feet flat or resting them on the floor or a footrest.
  2. avoiding crossing the knees or ankles.
  3. maintaining a small gap between the back of the knees and the chair.
  4. positioning the knees at the same height or slightly lower than the hips.
  5. placing the ankles in front of the knees.