That's an excellent and very practical question! As someone who's managed facilities and compared countless bins, I can give you a real-world perspective beyond the sales brochures.
Honestly, both can be durable, but they fail in different ways and under different conditions. It's less about which material is "stronger" and more about which is stronger *for your specific situation*.
Metal Bins (typically galvanized steel):
Their strength is legendary for a reason. They are incredibly resistant to impacts and won't crack in cold weather. A well-made metal bin can handle heavy, sharp construction debris without issue. Their main enemy is corrosion. Even galvanized steel will eventually rust, especially if the coating is scratched and the bin is exposed to salt (near oceans or from road de-icing). They can also dent, and the dents can trap water, accelerating rust. The bottom is a common failure point.
Plastic Bins (typically HDPE or resin):
Modern outdoor plastic bins are not like cheap toys. High-quality ones are UV-inhibited to resist sun fading and cracking, and they are inherently rust-proof. This makes them fantastic for coastal areas or places with high humidity. They are also lighter and easier to move. Their weakness is brittleness in extreme cold and potential degradation from prolonged, intense UV exposure over many years. A heavy, direct impact can crack them, whereas a metal bin might just dent.
The Verdict from Experience:
For high-impact, high-abuse areas (like behind a restaurant or on a construction site), a heavy-gauge metal bin often outlasts plastic. For general public use, parks, or coastal properties where rust is the primary concern, a thick, commercial-grade UV-protected plastic bin will frequently outlive a metal one.
The most durable choice often comes down to your local climate and what you're throwing away. Investing in a true *commercial-grade* bin of either material will always beat a cheap big-box store version. Look for reinforced lids, robust hinges, and thick walls. With proper care, both a good plastic bin and a good metal bin can easily last 10-15 years outdoors.