I've heard some people making the claim that the eupnea chest only method of breathing is not the best method of breathing normally.

I wondered what's the SS stance of how to breathe normally, as in when relaxed and not in danger or exercise.

Diaphragmatic breath is the most normal.

Diaphragmatic like Aquarius said and also since reading this from a post from Lydia this has been amazing for me, breathing in slowly (Not too slow) and for as long as comfortable and then exhaling naturally (Not holding back or forcefully).