Anti-shock or standard poles
Anti-shock trekking poles have internal springs that absorb shock while hiking downhill. This feature is especially useful for those of us who have problem with our knees, ankles, or hips. This is what I chose since I've had severe knee problems while backpacking downhill (Grand Canyon!).
Standard poles without the anti-shock feature are lighter and cheaper, and give the same kind of stability and balance.
While you can still probably find bamboo or wood hiking poles, most of today's hiking poles are made of aluminum or carbon fiber.
High grade aluminum poles are stronger and less expensive than carbon fiber trekking poles. If you're looking for super-light-weight poles, the carbon fiber poles are great. They're reasonably strong, although they may break under high stress.
Good quality hiking pole grips (handles) are usually made from cork, foam, or rubber. Cork may degrade more quickly, but is often most comfortable for the hands. Foam feels good, and absorbs sweat. Rubber protects hands more from cold and vibrations, but may chafe hands during hot weather.