That's Not How Science Works
We don't need an explanation for the Fermi paradox, because we have no evidence that needs explaining. We have a sample size of exactly one when it comes to life in the universe, and we can't draw scientific conclusions from that.
Of course, scientists love to speculate like everyone else, so lots of them have opined on possible reasons why we haven't spotted other civilizations. But until we have actual hard data to work with, none of this is scientific.
That said, some explanations are more grounded in reality than others. For example, speculating that a galactic civilization might destroy anyone who becomes known is just pure science fiction. On the other hand, exoplanet surveys, studies of supernovae and gamma-ray bursts may help us constrain some aspects of the issue and rule out certain reasons.
But as of now, there just isn't enough data to have 'scientific' theories, let alone have enough of them for one or more to be leading candidates. It's all just speculation and thought exercises now, and there's not even enough information to know which ones are better than others.
If you were to ask most scientists informally, I think you'd find that most of them suspect that life is common, based on the speed at which it appeared on Earth after it was capable of sustaining life, but that complex life may be very rare, given that it took billions of years to develop on Earth after single-celled life arrived. They might also apply the Copernican principle that the Earth is not special, so we should expect to find life elsewhere.
But again, with a sample size of one that can only be speculation.