There's no question that Sean Smiths cover skills are better than Allens but the reason he's not in the game is his run support. Which, if you look at the game film, was lacking against the Bengals yet again. So Sparano's quandry is which sword does he fall on. You've got a physical running team coming your way so my guess is Allen gets the nod again this week. I would expect Smith, at some point, to win this job back again I just don't think it starts in the next couple of weeks due to the opponent.
I am FAR less concerned about a Cornerbacks run support than his pass coverage ability. Like 100 times less. That's a no brainer decision if I ever heard of one.
Allen is little more than a nickelback. Let's treat him like one and let the true starter play as he deserves to play.