While faucet design is likely going to be a big factor in your kitchen faucet decision, the functionality of kitchen faucets comes down to five major components.
Mounting
Assuming you are purchasing a faucet for a pre-existing sink, you will first have to know how many holes are available for installation: one, two or three. If you have as many as three you can more or less choose whatever faucet you wish, as additional holes can be easily plugged if not used, but you can't install a faucet that requires more holes than your sink basin has. The number of handles on the faucet, as well as whether there are additional features such as a separate sprayer, soap dispenser or hot water filler all require additional holes.
There are a number of important considerations to make before buying a new faucet.
Neck
Gooseneck faucets are common, but even among them there are lower arc and higher arc options, and you should take measurements in your space to make sure you're not choosing something that exceeds the height of what's available. Straight faucets take up less vertical space and are generally less expensive, but leave less room in the basin for doing dishes or filling up pots.
Reach
Your faucet's ability to easily reach every corner of your sink also comes down to a matter of how it's intended to work. Pull-down faucets are the most common and consist of a sprayer mounted on a hose that can be pulled down from the arched neck, or remain locked in the arm of the faucet when not in use. Pull-out faucets are typically found in models with a lower profile, and pull forward from the base, rather than down, and usually include a longer hose. Stationary spouts, such as those in most straight-neck models, often include a separate sprayer attachment that is mounted on the side of the sink.
This professional faucet from Kohler gives you more reach than a standard model.
Handles
Single-handle faucets are the most common and contain only one handle for adjusting the water temperature. They are the easiest to install but can be tricky to adjust to your perfect temperature every time. Touchless or smart features, where available, are typically aligned with single-handle models. Double-handle faucets include separate handles for hot and cold water, allowing you more nuance to adjust the temperature to your liking and giving a more old-fashioned or farmhouse look. Double-handle faucets are tricky to install and require additional holes in the corresponding sink.
There is a huge variety of kitchen faucet styles and finishes to choose from.
Finish
Many faucets offer spotless or fingerprint-proof finishes, which usually consist of a brushed metal look, rather than a shiny look. Nickel, chrome, matte-black and stainless steel are the most common finishes, with bronze, gold and pewter as occasional options.