Agree on the fiberglass sheets coming unglued...
Aluminum is repairable much easier and will not de-lam.
Fiberglass sheets looks a lot nicer, but can de-laminate when water damage happens and might need to be re-glued or the entire sheet replaced, which is much more complex than replacing a single strip of aluminum siding.
IMPORTANT side note:
RV's are not build like a car. They need to be maintained yearly and at minimum every two years. The "caulk" needs to be re-done every year or two, or at least closely inspected and patched as needed. This is where 99% of the water damage occurs to RVs. This is typically the source of leaks on the roof and walls. LAP sealant is the "caulk". Never use caulk and esp never use silicone. Silicone works very well, but is very hard to impossible to scrape back off. Unless the rv is headed to the dump in the next two years, do not use silicone.
Scrape the old LAP sealant off, and put new on. Lap sealant is easy to scrape off, and this is why it is used for RVs