I like the sand as well !I have to speak up for the Sand color! It is just beautiful, sophisticated, and the picture on the Coach website doesn't do it justice.
However, I do love BOTH colors. For the next PCE (here's hoping), I have my eye on the Minnie duffel in Cognac and the regular duffel in Sand.
You really can't go wrong with either color, though. If it helps you make up your mind, I would guess that the Cognac color will be around for longer than the Sand will.