The best material often depends on the process used to build the item.
For casting, I'll mention Zinc or Zamak. Either is easy to melt, and it's fairly simple to electro plate for a chrome-like finish. It's what most chromed Water Faucets are made of. Really, it's what most castings are made of.
For machining, it might still be Zinc, but as I've never machined Zinc, aluminum should be mentioned. Anodize for finish. Although, I'd not ask a shop to anodize just one part. Too much trouble. You could always use polishing compounds, but the finish would be temporary.
It might be possible to polish a part and then seal it using some sort of plastic spray. Again, I've never seen that done.