“Two possibilities exist: either we are alone in the Universe or we are not. Both are equally terrifying.” - Arthur C. Clarke
This question is not more which you personally believe, but which would you would prefer be true. For example - I personally believe that humans are alone in the universe given the very unlikely and specifically required conditions that gave rise to us. However, I would prefer that we were not alone in the Universe and there were other developed forms of life across the universe. The former just seems so boring.