Repairing repeated cracks where two different wall materials meet

A hairline crack keeps returning where an old plaster wall meets a newer drywall section. I fill and paint it, and a few months later a faint line reappears. The two surfaces probably move differently with temperature and humidity. Would a flexible paintable joint, reinforcing tape or a different compound be more durable than another rigid patch? I'd rather acknowledge movement than keep hiding the same crack every season.