The squat (aka primal or Asian squat) would be better than sitting or standing to poo.

There is a lot of research on this... If you do sit, it helps to bring your knees up closer to your chest. You can buy devices to help do this... The Squatty Potty for example. Basically, things are better aligned (for sitters) when your knees or hips are bent deeply.

Other research shows the Thinker Position Statue is as ideal as the squat for pooping ease (if you are a sitter).