I actually think Beethoven's best work is better than Mozart's, and both are substantially better than Bach's, but that's really an artifact of history ... they each improved upon the previous master's work. Bach was the Godfather and clearly the father of classical music, and I love the simple beauty of his work, but it's simply not at the same level as the later classical/romantic composers.

Put them all in the same room at the same time, however, and I think Mozart would blow them away. The guy was probably the best definition of genius/prodigy our species has ever produced.