There are multiple aspects to your question, such as:
- Water conservation
- Lead content
- Carbon Footprint
- Resource consumption
Let's start with water conservation. The federal mandate is that kitchen faucets flow at a rate that does not exceed 2.2 gallons per minute.
Therefore, if you would like an environmentally friendly faucet you could consider a model that uses less than 2.2 gallons per minute. To find these low flow faucets you will need to go to individual manufacturer's websites such as Delta, Grohe, Kohler, Moen, etc. because the US EPA Water Sense Program is currently only rating lavatory faucets, not kitchen faucets.
That said, there are some draw backs to low-flow kitchen faucets - it takes longer to fill pots with water, sinks with suds, etc.
Don't despair, consider a sensor faucet that allows you to activate the faucet with either the knock of your hand or by passing your hand in front of a sensor. Delta has the Touch 2O model, Moen has the Moen Motion Sense and Kohler has the Sensate. These faucets can save a lot of water while minimizing the risk of bacterial contamination when you are working with foods such as raw chicken.
There is legislation, the Reduction of Lead in Drinking Water Act, which will go into effect on January 4th 2014.
Some manufacturers, such as Delta Faucet Company, elected to bring all their products into compliance in advance of the deadline. So look for products that are lead content compliant.
As a resident of the USA, consider purchasing products that are manufactured in the USA.
This can minimize the carbon foot print of the product as well as helping ensure that the manufacturing processes have a limited impact on the environment due to the stricter environmental laws in the USA compared to third world countries where a vast quantity of plumbing fixtures are manufactured.
If you want to get into the minutia, a single lever faucet will generally use less metal than a two handle faucet.
As for finishes, the environmental impact of all finishes is basically the same. Chrome is very durable and will give you long service, so is worthy of consideration.
Lastly, make sure that the guts of the faucet are ceramic rather than plastic, this will help ensure that your faucet has a long life and will not become fodder for the land fill.
Note: many plumbing product manufacturers have two or more tiers in their product lines. This means that they produce faucets that look identical on the outside but are not built the same on the inside. The lower quality products are often distributed through warehouse store.