Does the big bang theory or the steady state theory explain the origin of the universe better? Why?
The big bang theory is currently the best theory of how the universe was created.
The steady state model concluded that the observable universe was of a constant density because there was a source of matter in the universe generating new energy. At the time, the concept of matter being neither created nor destroyed was still new and contested. The theory of the big bang states that there is a constant amount of energy in the universe. All of this energy was created in the moment of the big bang.
There are several reasons the steady state theory is discounted. The first is the fact that the universe is changing. By looking through telescopes into deep space, we can see effectively into the past of the universe. At the furthest reaches of observable space, things are different. Radio wave-emitting stars, forming galaxies, and more varieties of stars can be found, suggesting a changing universe over time.
The steady state theory is also discounted because of cosmic microwave background radiation. This field of radiation is almost strictly uniform in wavelength and direction, showing no point of origin. This implies there is no point where matter is being generated and no point where energy is being created. It also aligns with the theory of a cooling blackbody, which the big bang theory suggested.
Newer data today still refutes the concept of steady state. The recent discovery of gravitational waves is evidence of colliding supermassive black holes from the time after the big bang. Even the concept of Hubble's Law refutes the steady state theory, as stars can be observed to have velocities away from the point of observation proportional to the distance away.
The big bang theory explains the origin of the universe far better than the steady state theory.