If I had to pick just one, I’d go with powder-coated aluminum furniture with sling or HDPE seats. It is the closest thing to “set it and forget it” for balconies, rooftops, courtyards, and small urban patios. The frame resists rust and fading, it is light enough to move when you clean or rearrange, and it does not need the regular oiling that teak does or the deep scrubbing that woven wicker often demands. Sling seats and HDPE boards dry fast, wipe clean, and do not hold onto dirt the way thick cushions can.
The real low-maintenance trick is to avoid overcomplicating the setup. Choose powder-coated aluminum instead of bare steel, pick a breathable sling or HDPE seat rather than deep foam cushions, and keep cushions optional or quick-drying. In a city, that matters because furniture may face pollution, rain, strong sun, and limited storage. A simple rinse with water, a little mild soap for sticky marks, and an occasional check of screws and feet is usually enough. Unlike wood, it does not need sanding or sealing. Unlike concrete, it is not painfully heavy to shift. Unlike cheap metal, a good powder coating protects the surface from routine wear.
For most urban outdoor spaces, powder-coated aluminum with sling or HDPE seating is the practical winner. It looks clean, handles weather well, and asks very little from you beyond a quick wipe-down now and then. If you want furniture that stays usable without becoming a weekend chore, that is the option I would recommend first.