Soft bags are more common than hard cover luggage. Soft bags are easier to squeeze into overhead compartments. They are lightweight and flexible for packing. You can choose a carry-on with a zippered backpack attachment, or a duffel that can be strapped to your back or wheeled through the airport. Hard cover cases bags are tough, heavy but not flexible. They are useful to protect your fragile items (camera equipment etc) better than soft bags.
Make sure you are paying for good quality. Have you experienced the quality of Swiss Army luggage?