Aluminum for structural design/support strength and long life together with the DECK made with real natural LUMBER milled from a TREE such as mahogany, locust, cedar, cypress, or the #1 most used deck material, pressure treated PINE.
Lumber can always get sanded, stained or painted and will look totally excellent for years and years.
Have you walked the .3-mile X 6'-wide long dock on the Laverack Nature Trail out behind the Meredith Village Savings Bank .....
www.youtube.com/watch?v=X2EqbiTpUXE ..... made with LOCUST lumber from South Carolina ..... and is totally not stained or painted ...... and two years, new!