Actually, Mazzilli's still been playing around with it. He seems unsure whether to go with the guy who runs better, but also hits for a low average (though he has a marginally good OBP and fouls off many pitches), or to the man who's been hitting better this season (with less speed). Check out the game logs...Hairston was given a short leadoff stint. If Roberts struggles, look for Jerry.
Objectively, I'd rather have Chad Cordero. By a decent margin, too. In addition, Roberts won't give you AVG. Hairston may give you both, but isn't the greatest basestealer. His average is decent, but certainly not the best. Can you swing a deal or something?