My preference is that, from the side view, the origin of the thigh bones and the origin of the hips/pelvis/spine appear to be at the same point. That way it's possible to tilt the pelvis forward and back without moving the legs.
In real life spines are curved, in CG people tend to simplify by making them straight.
The front to back placement of your spine depends on where the mesh of your character is, it doesn't have to be at zero.