Honestly, I’d start with powder-coated aluminum. It’s light, doesn’t rust like ordinary steel, and the coating protects it from constant damp and city pollution. Marine-grade stainless steel—ideally 316—is even tougher, especially near the coast or where roads are salted, but it costs more and shows water spots, so it needs wiping now and then.
For seating, teak is still one of the best natural choices. It has natural oils, handles rain well, and ages gracefully if it has good drainage and a little occasional cleaning. Recycled HDPE is the low-maintenance winner: it won’t rot, splinter, or absorb water, and good brands hold color well in wet weather. Concrete and stone work well for tables and benches because they’re heavy and weatherproof, though they can be cold and need sealed joints to prevent staining.
I’d avoid mild steel, untreated pine, MDF, and cheap woven wicker unless they’re specifically rated for outdoor use. Even with the right material, design matters: drainage holes, sloped surfaces, breathable covers, and quick-dry cushions make a huge difference. In a rainy city, the best furniture is not just water-resistant—it’s easy to drain, clean, and maintain.