well dom stands for drawn over mandrel meaning it is seamless tubing. hrew is rolled over and welded at a seam. so dom is stronger being one solid piece. you also have to think that the smaller the tubing, the less it will dent because there is less area inside the tubing for it to push in, and a smaller diameter means the tube is a tigher overall circumference which makes it stronger. also wall thickness comes into play. i use 1 5/8" dom, because it's unique and no one uses it. but i'd say use 1.5" dom with a .120 wall for toyotas, and heavier full size rigs (dodge chev ford) i'd use 1.75" dom with a .156 or .188 wall tubing.
