Honestly, if I were choosing a bench for a busy downtown sidewalk, I would skip wood and basic plastic. The best choice is a commercial-grade metal bench with a powder-coated or thermoplastic finish. Downtown sidewalks get constant foot traffic, weather, road grime, and occasional vandalism, so the bench has to be heavy-duty and easy to maintain.
A steel or galvanized frame with a surface-mount base is ideal. Surface mounting keeps the bench from being moved or stolen, which is a real problem in active public seating areas. Look for vandal-resistant hardware and tamper-proof bolts. A slatted metal or coated steel seat drains rainwater, dries quickly, and doesn’t trap dirt or food. Wood can look nice, but in a high-use downtown sidewalk setting it weathers, stains, and needs more upkeep.
For most city sidewalks, a 6-foot bench with a backrest and maybe a center armrest offers the best balance of comfort, durability, and space. It gives people a real place to rest without encouraging sleeping or loitering. If the sidewalk is narrow, choose a backless bench or a shorter 4-foot model, but keep the same commercial-grade construction.
So my pick is a surface-mounted, heavy-duty park bench with a galvanized steel frame and coated metal slats. It is not the cheapest option upfront, but it will outlast cheaper public seating and stay presentable on a busy downtown sidewalk.