Is it better to have positive or negative airflow?

Whether it is better to have positive or negative airflow depends entirely on what you are trying to protect, the people inside the room or the people outside the room. Positive airflow, where air pressure is higher inside the room than outside, means air flows out of the room when doors open, which protects the person inside from outside contamination. This is used in operating rooms, protective environments for immunocompromised patients like chemotherapy patients, and clean rooms for manufacturing, where you want to keep germs out. Negative airflow, where pressure is lower inside, means air flows into the room and not out, which protects people outside from contamination inside. This is used for airborne infection isolation rooms for TB, measles, and COVID patients to keep infectious air contained. In a home HVAC system, slightly positive pressure is generally preferred to prevent unfiltered outside air, dust, and humidity from being sucked into walls, while in water damage restoration, negative air machines create negative pressure to contain mold spores during remediation so they don't spread to clean areas. Neither is universally better, they serve opposite goals. In computers, positive pressure reduces dust buildup. In homes, balanced airflow with equal intake and exhaust is often ideal for comfort and energy efficiency, avoiding both excessive positive pressure that wastes energy and negative pressure that causes backdrafting of furnaces and carbon monoxide risks.