I think the best of the available alternatives for "atheist" is simply "non-theist." It lacks the strong connotation that there's definitely no God, and it could therefore easily be embraced by teapot or tooth-fairy agnostics.
Carece de la fuerte connotación de que definitivamente no hay un dios, y podría ser fácilmente aceptada por agnósticos de tetera o leyendas de ratones de dientes.