It's really personal choice.
I've owned both and the wood is warmer and does not transfer cold thru the studs. It expands and contracts with the weather, where alum would crack.
What kind of exterior skin do you like ? Vacuum bonded Filon or alum corrugated skin ?
As far as I know , vacuum bonded filon goes with alum frames. You would need more aluminum framework than wood framework to support the filon walls. Therefore, the added weight of extra aluminum and the heavier filon and glue makes the alum framed trailer, heavy. Wood frame can be 16" on center and aluminum corrugated skin which is much lighter than filon can be used.