Steel and aluminium are the two most common frame materials on everyday bikes, and each brings real trade-offs rather than one being objectively better.
Steel is heavier but flexes slightly under load, which many riders describe as a smoother, more forgiving ride over rough surfaces. It's also easier to repair if it ever bends or cracks, since steel can be welded relatively simply. The trade-off is weight and a slight tendency to rust if the paint is chipped and left untreated.
Aluminium is lighter and doesn't rust, which is a real advantage for a bike ridden in humid or wet conditions. It rides slightly stiffer than steel — efficient for pedalling, but transmits a bit more road vibration. For most everyday riding, either is a perfectly durable choice; the difference is a feel preference more than a right answer.