Step 1: Identify the comparison scope: "of all dresses in the shop" signals more than two items, which always calls for a superlative form. Step 2: Eliminate "the better" and "the very better," both comparative forms meant for exactly two items being compared. Step 3: "The very good" is simply the positive degree with an intensifier and cannot express a comparison at all. Step 4: Only "the best" correctly expresses that this dress surpasses all the others in the group. \[\boxed{\text{the best}}\]