Best of Three Worlds?

I am a Columbia grad who is in the middle of the first of two federal clerkships. My first clerkship is with a district court, my second, with a prestigious judge on a U.S. Court of Appeals. After the completion of my clerkships, I plan to return to New York, and to go to work for one of three firms. I am interested in developing a career as a firm litigator, and I am also interested in eventually leaving private practice (at least for a few years) to go to a U.S. Attorney's Office. Can you help me choose between three diffferent offers from firms?