That's a great question many city planners and facility managers ask. The short answer is: it depends heavily on the specific use case and environment, as both have distinct strengths.
Metal bins, typically made of galvanized or powder-coated steel, are famous for their sheer structural strength and weight. They are extremely difficult to tip over, can withstand significant impact (like from a vehicle), and are highly resistant to chewing or damage from animals. However, they are prone to rust if the coating is scratched, can dent, and their paint may fade over time. They're also heavier to move and can get very hot or cold to the touch.
Modern plastic bins, made from high-density polyethylene (HDPE), offer different advantages. They are completely rust-proof, making them ideal for coastal or high-moisture areas. They resist dents, graffiti is easier to remove, and they don't require painting. The plastic is also a poor conductor, so they don't get extreme temperatures. Their main weaknesses are susceptibility to cracking in very cold temperatures if impacted, potential fading from prolonged UV exposure, and they can be melted by extremely hot debris.
For overall longevity in harsh, high-abuse settings (like a busy downtown street), a heavy-duty metal bin often wins. For general park use, coastal walks, or areas where rust and low maintenance are priorities, high-quality plastic bins are exceptionally durable and often the smarter choice. The best decision weighs factors like climate, vandalism risk, budget, and maintenance resources.