Kiln dried untreated Douglas Fir 2″x4″ (actual 1.5″x3.5″) lumber is specified to weigh 1.28 lbs per linear foot. This can change with prolonged exposure to humidity and variation in suppliers, species, and other variables.
1″x1″x.065 seam weld ASTM steel tube is .814 lbs per linear foot.
With ends fixed, the calculated deflection for a 4′ section is 0.218″ with a center load of 100 lbs.
For the 2×4 beam, it’s a little different because it’s a rectangle.
Positioned so the farthest fiber is vertical, a 4′ section with the same 100 lb point load in the middle would flex 0.4 inches. FF positioned horizontal you’re looking at somewhere around 2.2 inches of deflection at the load point.
So, for a nominal length, the 1″ square steel tube in any orientation is about as strong as the 2×4 is in it’s strong orientation when given a static load.
Remember that is not a linear relationship, and a longer section of 2×4 oriented FF vertical may flex less than the same length of tube.
Steel weighs less per linear foot.
I would also hold some other assumptions, listed here:
The steel has a higher propensity to bend and not come back to it’s original strength, so +1 for wood
Wood can get wet, mold, splinter, and is far more difficult to control. +1 steel
Steel can rust. +1 wood
Wood requires more “technology” to anchor together properly. +1 steel
Wood is easier for average folks to work with. +1 wood
Steel is easier for me to work with than wood +1 steel. (I can weld steel with the same ease as hot gluing popsicle sticks together)