First, each style can be very attractive design wise. A pullout kitchen faucet usually looks a little more traditional with a straight, slightly angled spout. A pull-down faucet with a high arching spout can look a little more contemporary.
Next, for mixing valves, the pullouts in most cases use a one-handle valve located at the top of the faucet body with the spout going out horizontally. Pull-down valves, on the other hand, are mostly located on the side of the faucet body with the spout continuing up vertically.
As far as spray heads go, pullout heads can feature large handles that work great for filling vessels on the counter. Pull-down heads can be smaller and sleek, and they work great for washing down the sink.
Bottom line: Choose the kitchen faucet that fits you best, and I’m happy to help you understand some of the ins and outs, ups and downs of choosing a pull-style kitchen faucet.