Most people pick an outdoor light the way they pick a doormat, whatever is closest to the door at the hardware store, and then wonder two winters later why it has gone cloudy and streaked with rust at every seam.
The difference between a metal fixture that holds up and one that doesn't comes down to a handful of things you can actually check before you buy. Solid cast or extruded aluminum and copper will outlast stamped steel by decades, because steel needs a perfect paint or powder coat seal to survive outside and that seal always has a weak point eventually, usually right at a screw hole or a welded joint. Look at how the pieces are joined. Cheap fixtures are often held together with tiny visible screws and a bead of glue you can feel if you run a finger along the seam. Better ones are cast as fewer pieces or joined with hidden fasteners, and the glass sits in a proper gasket instead of just resting against bare metal. Finish matters just as much as material. A good powder coat has some depth to it and won't scratch through to bare metal if you catch it with a key. A bad one is thin and shiny and chips if you look at it wrong. When it arrives, check the weight first, a light fixture that feels hollow and rattly is telling you something. Check that the glass or acrylic panels sit flush with no visible gap, run your hand over any welds, and make sure the wiring compartment has a real rubber gasket, not just a foam strip that will compress to nothing after one rainstorm. In place, metal fixtures sit best against brick, stone, or a painted wood door, something with enough texture that the fixture reads as a detail rather than the only thing on the wall. On plain vinyl siding they can look a little stranded, so size matters more there, bigger and heavier reads intentional, small and dainty reads like an afterthought. Over time, a well made one develops a bit of a patina that actually looks better with age, especially in bronze or copper finishes, while a cheap one just looks tired, chalky, and eventually spotted with rust blooming through the coating. Living near the coast speeds all of this up considerably, salt air is brutal on cheap finishes in particular.
Expect to rehang or at least retighten mounting screws after the first year, since wood and siding shift with the seasons and a loose fixture is how water gets behind the backplate.
Wipe the glass and housing down twice a year with mild soap and water, nothing abrasive, and it will keep looking like you meant to buy it.