These are mine. Made them out of gal and folded plate:
I haven't had any trouble with sticks getting caught up on the underside and the 4x4 has dropped down on them a handful of times now without any signs on bending. My last trip I slid the whole drivers side along a rock ledge whilst trying to get the rear tyre back on the ground (typical MN long arse troubles) and only damage was paint removal.
Went with box section because I have to stand up on them daily to put x2 kids in carseats in the back. My last 4x4 had tube with flat on the top and I slipped on the outer lip often.
My rear bar is thick walled tube and also cops its fair share of knocks. Which is better, I cant tell. Built strong enough, they will both do well IMO.
If you are shopping for an off the shelf item, try and find something that runs the entire length of the cab and as far back as possible. There is a Triton is town running MCC or TJM (cant remember which) and they look a bit too short IMO.