Although there are many factors that affect the performance of a golf ball, two of the most important are cover hardness and overall compression. In essence, the hardness of a cover (measured by an industry standard called the "Shore D" rating scale) influences how much spin a ball will have: The softer the cover, the more it will spin. (Some high-end balls have two covers -- an inner cover or mantel and a very thin outer cover. Each of these outer layers has its own properties and in combination further affect the overall performance, depending on how hard the ball is struck.)
Compression -- how "squeezable" a ball is -- influences feel and plays a role in generating distance. The firmer the core, the higher the initial ball speed. A soft-core, low-compression ball will generate lower spin and improve feel. Golfers with slower swings may find they can optimize their distance with a lower-compression ball; fast swingers can benefit from lower-compression balls as well as higher-compression models.
Below is a guide to the cover hardness and overall compression of some popular models, based on data about the balls' construction provided by the companies that manufacture them. By Scott Smith