I'll come right to the point. I think the works common attributed to William Shakespeare were actually written by ... William Shakespeare. The arguments for other authors generally boil down to snobbery about class or education level, and ignore that Shakespeare's earliest plays are really not all that great, to put it kindly. There are seeds of greatness there, sure, but they wouldn't be widely known or read if Two Gentlemen of Verona was all of his work that survived. Shakespeare learned the craft of writing by writing, not by education. And as far as class goes, most of the plays produced by the upper classes focus on the upper classes almost exclusively. Shakespeare covered a full spectrum of the human experience, irrespective of class. To me, that argues for someone with experience of both upper and lower class life, Shakespeare's biography fits that criteria better than most of the candidates put forward.
But there's a book out that suggests a new candidate for the authorship of Shakespeare's plays, and I'm at least curious enough to want to read it. The candidate is Mary Sidney Herbert, Countess of Pembroke.