From his comments here, it seems that he prefers the Flat Tax because it's easier to pass.
But he recognizes that the Fair Tax dismantles the control structure of the political class. He knows it's a better plan for America on the philosophical merits of tax policy.
He actually touched on that back a couple months ago.
Basically said he'd like to see either, but the Flat Tax had a better chance of passing.
He said also that neither one has a great chance currently because the power of taxation is the single greatest power Congress has.
In other words...he said the same today. Rush is consistent!!