According to Eat This, Not That: The Best & Worst Foods in America, the best sandwich is Subway's 6" Double Roast Beef with all the fixings on 9 Grain Wheat.

Why double the meat? Because for an extra 50 calories, you get nearly twice as much metabolism-spiking protein, which helps build muscle and burn fat. Plus doubling up on a 6-inch sub will save you 220 calories over the other alternative for hungry sandwich hounds: the dreaded footlong. Get your money's worth by loading up on the free veggies: peppers, olives, onions, tomatoes, and spinach.