Wood and metal drawer slides are both excellent choices for building a drawer. The option that will work best for you will depend mostly on the weight capacity the drawer will have to bear.
The biggest benefit to metal drawer slides is their exceptionally smooth sliding motion. This is due to the use of wheels and ball bearings which allow the drawer to slide in and out with very little friction. Wood drawer slides, while perfectly usable, do not slide with as much ease as metal drawer slides.
Wood drawer slides have the advantage of much greater load capacity than metal. When considering wood, bear in mind that harder woods such as oak offer a smoother motion and greater load capacity than the soft woods. Metal drawer slides will always have a lower total weight capacity than wood, although the weight capacity will vary depending on the size and type of slide.
The main consideration in determining whether to use wood or metal drawer slider is the use to which the drawer will be put and the weight it will have to bear. If it is likely to contain extremely heavy objects then wood is automatically a better choice. If weight is not a concern, metal will provide a much smoother motion and be less prone to wear over time. See manufacturer's specifications for the actual weight each kind of slides can bear.