The best all-around choice for an urban planter box that has to survive winter is fiberglass-reinforced plastic (FRP). A quality FRP planter is made with a UV-stable gelcoat, a thick wall, and molded drainage; it does not absorb water, so freeze-thaw cycles are far less likely to split it. It also resists road salt, corrosion, and rot, and it stays lighter than concrete or steel. No material is truly crack-proof, but FRP comes closest when the box is properly designed and installed.
High-density polyethylene (HDPE) is a good budget alternative. It is impact-resistant and won't rot, but thin HDPE can become brittle in extreme cold and may fade or warp unless it is UV-stabilized. Powder-coated steel and aluminum are durable, but scratches and trapped water can lead to rust or ice expansion; use a flexible liner and drainage if you choose metal. Concrete, terracotta, and untreated wood are poor choices in freezing climates because they absorb water or crack under freeze-thaw stress.
For any winter-ready urban planter, choose a raised box with drain holes and feet, add a drainage layer, and avoid overwatering in late fall. Use a quality fiberglass planter with a UV-stable finish, and your box should handle winter far better than most alternatives.