Arguably, the best made keyboards available today have mechanical key switches. They are known as mechanical key switch keyboards. What makes them so desirable is that mechanical keyboards tend to be constructed of higher quality materials, they last longer, are more reliable, and most importantly, once properly acclimated to one, a mechanical key switch keyboard will make you a better typist. The vast majority of keyboards included with white box systems or sold at office supply stores are rubber dome or membrane keyboards. They are inexpensive, mass produced, relatively low quality devices that are inconsistent and degrade the user experience.
The differences between the various mechanical switch keyboards you're likely to come across are subtle, but definitely perceptible. Buckling springs are the type of switch used in the original "killer" mechanical keyboard, which still has a loyal following today, the IBM Model M. Buckling springs are still used in many of Unicomp's keyboards, like the Customizer 104. Buckling spring switches have a coil spring supporting each keycap that buckles or collapses, at a certain point when pressed, which provides auditory and tactile feedback to the user. The keys are usually fairly firm, but improve the experience immensely. Read more about mechanical key switch keyboards at HotHardware.