If your priority is battery life and silent operation under most loads, the M3 MacBook Air wins. The Yoga 9i offers more versatility with its 2-in-1 design and a potentially better screen for media consumption depending on the specific panel, but it won't match the Air's efficiency. For software development, both are capable, but the MacBook Air's macOS environment is often preferred by developers. Consider if you need the pen input and tablet mode; if not, the MacBook Air is likely the better choice for your described needs.