In my experience, DOM will dent just as easy as HREW. My cage is made of 1.75,.120 wall HREW. I wheel with several DOM cages, and they get bent up just the same as mine. We wheel pretty hard, flopped countless times, and I have no doubt my cage is just as strong. The design of the cage is more critical than the manufacturing process of the tubing. The only difference IMO, is the money I saved in tubing. (3.79/ft for DOM vs. 2.27/ft. for HREW)
If you want more dent resistant tubing, go with .134 wall down low, but price and weight go up exponentionally.
Come up with a basic design before you start bending. If built right, you can use less tubing with the same amount of protection. Most exo's I see have too many tubes and have the "jungle gym" look.
To each his own, but I like to keep it simple.
My cage is only to protect my noggin, and the windshield in that order, the rest is sacrificial
