Since all retail CPUs are boxed with perfectly good coolers (which are pretty quiet), the main reason to buy an aftermarket cooler is its performance when your processor is overclocked. (There might be some who buy coolers based on the aesthetics of their appearance through a windowed CPU case, but we"ll assume they"re in the minority.) But while performance is certainly the main criterion, other factors must be taken into consideration as well, such as noise, size, other features, and price. The ideal cooler keeps your processor at or near ambient temperature, is silent, free, and unfortunately doesn"t exist. Manufacturers vary the performance, noise, size, features, and cost factors of their products to address different segments of the market.