Given the choice I would choose aluminum every time. It is easier to repair and hides imperfvections better than flat pre fab sandwich board which, IMHO , is for a faster prduction time and little else. When the RV industry comes up with something new it is usually for their benefit. Not the consumer. I paste wax my HTT once a year and have found Mcguire's carnuba wax to be the best. My rig is 13 years old and shines better than new. Sadly I did not have a siding choice and it has sandwich board which has held up pretty well, though it is very boring in appearance. Best of luck