For metal garden benches UK shoppers, the most practical choices are powder-coated steel and cast aluminium. Both handle damp spells better than untreated iron, and they work well with cushions because the frames stay firm and stable. Aluminium is particularly useful in smaller gardens where you might want to shift the bench between sun and shade.
One detail worth checking is how the frame copes with rainwater. Open slats, curved arms and raised legs tend to dry faster and gather less grime than ornate designs with tight scrollwork. That means less wiping down before the cushion goes back on, especially after a typical UK shower.
If your garden is exposed, darker matte finishes usually hide water marks and minor wear better than glossy paint. It is also sensible to pair metal with a cushion that has ties or a non-slip base, since smoother seats can let lighter pads drift about on breezier days.