Metal, don’t get the metal coated plastic ones that the big box stores sell. You will have the best selection at an independent plumbing supply store and they have trained people to guide your selection.

Heavy brass that has a PVD coating of whatever metal on top.

For a quality faucet look for as much metal in the construction as possible. For the finish/color you can't go wrong with chrome or brushed stainless.

I like the brushed stainless because it matches the stainless steel kitchen sink and any stainless appliances, so one less finish to worry about. Kohler calls that finish Vibrant Stainless.

There is no difference between the same brand and model faucet sold at a big box as opposed to your local plumbing supplier. None.