Round is the better pick for anything wet or bowl-shaped: soups, curries, grain bowls, chili, oatmeal. There are no square corners for sauce to hide in, so they rinse clean in seconds, and they nest more tightly than rectangular ones when empty. Rectangular containers use fridge and freezer shelf space more efficiently and suit a plated main-and-sides layout better. If most of what you pack is scoopable rather than plated, round is the right call.