Aluminum sides are easier to repair if the wall is damaged. Fiberglass suffers from Delamination...always...every fiberglass camper will eventually delaminate to some degree or another.
My personal preference is the corrugated aluminum. Admittedly it doesn't look as slick but it is reliable and if you get water damage in the wall and the wall has to be repaired the repair is invisible as the aluminum covers the repair.
The flip side to that is that aluminum can hide damage for a long time until us shows on the interior.
In reality, if either are maintained then they last a long time. If either is not maintained then they will degrade very quickly.
BTW...Jayco uses aluminum on its Jay Flight and Swift series and uses the fiberglass on its Hummingbird, Jay Feather, Eagle and Whitehawk lines
Thanks!
Jeremiah