I will be buying a new kitchen faucet soon and am wondering about the pull-down sprayer. I use my sprayer often and have reservations as to whether the pull-down style will be easy to pull down and if it will keep its retractability.
The pull down you refer to, I assume, is being able to grab the nozzle of the faucet and pull it out, correct? Longevity will depend on the material the hose is made from, some are metal clad, some are not, you'll need to inspect the faucet before you buy to know what your model will have. Metal clad should last a very long time, as the cladding will protect the hose itself from wear. If the hose does not have some sort of cladding, metal or otherwise, it will deteriorate in short order.
Stick with good quality, name brand faucets and you shouldn't have any issues, buy an off brand and you're on your own. In answer to your next question, Delta and Price Pfister are leading brands, Moen too, if you're a fan, I am not.
We can't stress this enough: buy only Delta/Peerless or Pfister - they have every design there is on the market, plus a solid customer service and warranty for parts.
No faucet can last forever, but these manufacturers have proven their loyalty and dedication to their customers.
And no, I don't get paid for endorsing them.
The type where the hose pulls out of the pipe are going to give you trouble in the long run. Mostly it will be from stuff stored under the sink that tends to get in the way of the excess hose when you try to retract it. I would recommend a faucet like one of these which has less moving parts to deal with. A true commercial one would be the best, but they require a lot of head room above the sink. A 20 to 26" unit should work well in a home kitchen.
You may find similar units at your larger Home Depots and Lowes.
There are two basic styles: pull down which has a smallish nozzle at the end of the hose, and pull out which has a wand with the spray coming out 90 degrees to the handle (kind of like the handheld shower units).
The pull-down style is really only useful if you have a deep sink. If you have a shallow sink, pots and pans might be too close for you to get the hose pulled down and out. Stuff in the sink gets in the way. Even if you do get a pull-down style, make sure the bottom of the spray nozzle actually is higher than a standard faucet -- some are not. The high arc looks impressive, but it ends up with no more clearance under the spout than a regular faucet.
If you fill a lot of pans on the counter or buckets on the floor, a pull-out style will be easier to use.
(It's probably obvious that I prefer the pull-out style over the pull-down style.)
And I second the recommendation for Delta or Price-Pfister. A good-quality faucet will set you back at least $200, maybe as much as $500. Brass ain't cheap, and metal-body faucets are labor-intensive to make.
The hose can get tangled on the shutoff valves under the sink. That can be very annoying.