Yes, in most real-world situations a concrete street bench is more stable than a wooden one. The biggest reason is mass. A typical concrete bench can weigh several hundred pounds, which gives it a low center of gravity and makes it much harder to tip, slide, or push out of place. A wooden bench, especially a lighter slat-style bench, can be shifted more easily unless it is bolted down or fitted with a heavy steel frame.
That said, stability is not only about material. A well-built wooden bench with a steel or cast-iron base anchored to a concrete pad can be extremely stable. At the same time, a concrete bench placed on soft ground, loose gravel, or an uneven surface may rock, tilt, or slowly settle over time. So the honest answer is that concrete usually has a natural stability advantage, but installation and foundation matter at least as much as the material itself.
Concrete also tends to hold its structural stiffness longer in public spaces. It does not warp, rot, or develop loose joints the way wood can after repeated rain, sun, and temperature changes. Wooden benches can become wobbly when screws loosen, boards cup, or joints swell and shrink. In cold climates, freeze-thaw cycles can cause surface spalling on concrete, but that rarely affects overall stability as quickly as wood rot or joint failure does.
Another factor is daily abuse. On a busy street, benches get sat on heavily, kicked, pushed, and sometimes vandalized. A concrete bench is far more resistant to being moved or broken. A wooden bench may lose slats, crack, or become unsteady after rough use. Even a heavy wooden bench can develop side-to-side sway if its joints are not maintained.
If your priority is a bench that stays put with minimal upkeep on a public street, concrete is generally the more stable choice. If you prefer the look of wood, choose thick lumber, a heavy metal frame, and proper anchoring. For most public or high-traffic areas, a reinforced concrete bench offers the best combination of stability, durability, and low maintenance.