What brake pads you want to buy for your car depends on several different considerations: what kind of car you have, what your budget is. Do you prefer quiet brakes, more efficient ones, which wear less on your rotor? Because of this, there is no easy "this is the brake pad you want" answer; however, some pads do offer better quality than others. This article is not a breakdown of what brands and manufacturers are out there, but rather a general overview of the four different types of brake pads commonly available.
Generally the cheapest brake pad you'll find in any auto parts store, non-asbestos organic (NAO)--or just "organic"--pads are constructed from, surprise, organic materials such as Kevlar and carbon. These pads are softer and create less noise when braking, but also wear out faster and kick up more braking dust due to their less resilient materials. They are generally considered of poorer quality among qualified mechanics, and are usually only recommended if cost is an issue, and long pad life is not.
Low Metallic NAO
Found most often in European cars, low-metallic brake pads are pretty much what their name suggests. Similar to organic pads in that more than half their composition is made up of organic materials, low-metallic pads also include small amounts of copper or steel to add to the resilience of the pad. Low-metallic pads provide decent braking action, but can also be noisy and wear out quickly, albeit not as quickly as organic due to the added materials. Users also often complain that the brake pads leave a black residue on alloy wheels, so factor that into your decision as well.
The semi-metallic pad is not as popular with motorists these days as it was in the past, and the reason for that is one simple word: noise. The semi-metallic is constructed from steel and other metals, and while it offers good performance and wears out more slowly than the organic brakes, it is also often noticeably louder than the organics. It also tends to wear harder on your rotor, which is another factor you ought to take into consideration. Still, if you don't mind the noise, the semi-metallic is a good all-around brake pad, and usually quite reasonably priced.
Ceramic pads are generally considered to be the best in quality of the four types of pads. Quieter than semi-metallic, cleaner than the organics, and the composition of the pad allows for a smoother, more consistent braking "feel." They also tend to wear out slower than the other three pads, although their performance is lowered at higher temperatures. They are also the most expensive brand of pad, usually costing up to twice as much as any of the other kinds. Still, if quality is what you're after, and you don't mind paying the extra money for it, the ceramics may be right up your alley.
This is only a very general overview of the four types of brake pads most commonly stocked in auto parts stores; there are dozens of brands out there, and the composition and effectiveness of each brand will differ from one to another. To find out what pads are best for your specific car, consult a qualified mechanic, or your local auto dealer to find out what originally came with your vehicle. Chances are, those will be the most effective kind you can get.