Fibreglass or aluminium

Or better off with aluminium if you scratch it badly.

Personally I would be more concerned with floorplans than outside coverings as that subject ranks up with the Nissan vs Toyota debate.

Both have pros and cons so its up to you to decide which is best.

Even talking to my friendly van repairer you would get the same answer as he has a similar number of each in for repair.

He did have one brand new glass van in last year that was half way on a round the block trip. They had to strip and reseal the whole van, windows door, everything due to the extremely bad job done on sealing it.
When he showed me they had not taken the shine off where the sealant was applied and it had all pulled off on the first trip allowing the whole back wall (which was of sandwich construction) to get soaked and as it only had cardboard waffle holding it apart it had collapsed.
This of course could happen with alloy as well.
Suggest you talk to someone like him, he can tell you the good and bad of just about any make on the road.

We are in North Brisbane if that helps.