You suggest that Big Bang and Hoyle’s Steady State were the main competition. The discovery of the Background Radiation was claimed to be the decisive factor in favour of Big Bang, yet there was a possible better explanation for it. ‘Better’ in the sense that it gave more accurate predictions than those of Big Bang theorists. I quote an earlier article of mine: “Alpher and Herman predicted the existence of the CMBR in 1948. In 1933, however, the German physicist Erich Regener had predicted the existence of a microwave background produced from the warming of interstellar dust particles by high-energy cosmic rays, thus not a product of a Big Bang”.

For full details, including the better predictions, see: https://medium.com/@graham.pemberton/did-the-universe-begin-with-a-big-bang-part-2-possibly-probably-not-d4d492959f8d

It is also worth noting that several professional scientists are now beginning to doubt Big Bang theory, saying that it now no longer matches observations. There were articles on this theme in New Scientist last year. I wrote an article which summarised them: https://medium.com/@graham.pemberton/did-the-universe-really-begin-with-a-big-bang-further-developments-6bcdf4d8d256

I received this interesting reply to that article: https://medium.com/@billwesley/this-is-a-serious-theory-by-a-phd-physicist-who-worked-for-nasa-that-features-relativity-playing-e3e389514b64