I don't think anybody will find a reliable source that states the mask wearing is more important than hand washing for the person wearing the mask and trying to prevent catching Covid-19. This article from ABC 4 oddly enough titled hand washing better than masks states the following.
Dr. Gary Cianci , M.D. with Roper St. Francis, says the general population typically turns to medical masks during large outbreaks of influenza, or most recently, the coronavirus.
He emphasizes that masks are most effective in helping prevent an airborne illness from spreading, rather than for protection.
“Medical masks do seem to help prevent the spread of viruses, but they don't do it necessarily in the way we expect them to,” explained Dr. Cianci. “They do several things. One is, the person who is wearing the mask, if they have the illness, that's the most effective way to prevent the spread.”
Once again I will state that the mask protects the other person.