It really come down to what you like. As shown each has it advantages and draw backs.
From the industry standpoint aluminum is old technology, well understood and lends itself to basic trailer designs. Fiberglass is a newer technology but still decades old. The big advantages are, it lends itself to more dynamic shapes, a so called "clean" look and offers a large easel for artwork graphics.
Aluminum dents and Fiberglass de-bonds, I have had both and the outside skin makes little difference to me. Floor plan is everything.
However, if you like snazzy, you are more likely to find it in a fiberglass trailer. If you prefer no frills and basic time honored construction, aluminum is hard to beat.