It depends on how you are using those two materials.
Concrete has incredible compressive strength but it has very little to no ductility or flexibility. Concrete, done correctly, continues to get harder with time, up to about one hundred years. Because it is so inflexible, concrete is usually reinforced with other materials. Concrete is often reinforced with synthetic fibers that are mixed into the wet concrete and this inclusion aids the strengthening of concrete by giving it a secondary way of absorbing weight or stress from loading. Reinforcing bar (or “rebar”) is often placed in concrete forms to bolster the overall strength of a concrete structure by pouring wet concrete into the form and encasing the rebar inside the concrete. This construction technique greatly increases the flexibility and strength of a concrete structure.
Steel, on the other hand, has intrinsic strength completely on its own. Steel has a very high strength to weight ratio and can absorb great amounts of load weight in compression as well as in tension. Steel shapes can also move in a tortional way without permanent deformation, at least to the yield point of the steel in question, unlike concrete which would crack and crumble under the same scenario.
The greatest difference between the two lies in steels ability to bend, flex and return to its original shape without deformation, in addition to very high load carrying capability. Concrete can certainly hold a lot of weight when loaded in compression but when that limit is achieved, it wil crack and be compromised. A good way to illustrate this is to look at the performance of the two materials in earthquakes. Steel structures can bend and move in earthquakes but concrete structures will repeatedly fail, crack and become unusable.
So the correct answer to your question lies in how the two materials will be utilized. They both have very specific characteristics and their uses must be carefully selected based upon those material’s special capabilities.
Hope it helps.