When it comes to performance, most players will tell you that the majority of the playability in a cue will be in the pool cue tip and the ferrule. The ferrule is that little white piece just below your tip at the top of your shaft. At its most basic level, the ferrule is your pool cue's shock absorber. Like a car's shock absorber, the ferrule provides an additional level of control over your pool cue. This results in an even flow of energy transfer throughout the cue. As you can imagine, if you chip or fracture your ferrule, you'll lose consistency and control.
Most cues being made today come with either linen fiber, Ivorine III or Aegis ferrules. Custom cues on the other hand, will often come with ivory ferrules which are thought to provide the most feel. Aegis and Ivorene are considered the best alternative to ivory and can be found in most cue brands including Joss, McDermott and Viking cues.
Knowing which ferrule is right for you is dependent on your style. If you're looking for a ferrule that will provide more feel and resonation throughout your cue, ivory or a synthetic ivory (Ivorine or Aegis) will likely be your best bet. On the other hand, if you want a ferrule that absorbs most of that feel and vibration, linen fiber ferrules are likely your better bet.