Most soccer backpacks come with a zippered bottom ball pocket that can hold a size 5 soccer ball inside, water resistant bases, and enough center space to carry all your warm-ups and extra socks. We love the fact that most come with a separate compartment for those smelly shoes. Not as much space as a duffel bag, but easier to carry.
Soccer duffel bags are designed to have 1 big compartment and to be carried in the hand or on the shoulder. They come with a ventilated side pocket for dirty shoes and a smaller zippered pocket for valuables on the inside. Better if you have more gear to transport.