I guess it depends on what YOU want.
We have aluminium for our annex. It's what came with the camper. They are very lightweight which means in a horrid blow they MAY bend and disappear over the horizon, but they are very lightweight which is a plus. A plus on these is that there is no wing nut to stop them going into where they are meant to go so the storage area is smaller. No issues so far.
I used to have steel ones with the wing nuts. They are heavy and heavy duty. They don't tend to bend very readilly, in a horrid blow they will still bend but you won't have to walk to the horizon to find them. The wing nut makes them harder to store as you must take the wing nut into account which means more room ... it also gets caught on things ... but it's great for hanging things from. No issues except in sand where mine got rather hard to use due to the sand getting in between the two lengths.
I guess it's a trade off ... lightweight against better stength.
Personally, I'd take lightweight every time. It means more
can be fitted to the vehicle.
Kit_e