The very short answer to this question is probably that it is a matter of personal preference. There is a bit more to deciding which needles are the best to use, so I am going to do a small comparison here. The decision can also be influenced to some extent by the type of garment or project you are making.
A number of years ago I worked in a shop which sold yarn, fabric, sewing machines and haberdashery. Amongst the many things I learned from my work colleagues was a lot of information about yarns and knitting needles. At that time the ranges of straight single pointed needles available included metal, plastic, steel lined plastic, and bamboo. There were also some circular needles and sets of four short double pointed needles.
I have never been a fan of metal needles. I find them hard on my hands and rather noisy to use. They are, however, very durable and resistant to damage. Plastic needles are light weight, cheap, and a good choice for beginners, especially children. They do have a tendency to break though, so I would not recommend them for large, heavy pieces of work, or for complicated patterns which may put a bit of stress on the tips of your needles.
Steel lined plastic needles combine the strength of metal and the more user friendly plastic surface. They are often colour coded for different sizes which can be very convenient when you are trying to sort out needles. I have also seen some of these needles with very decorative patterns on them. Obviously this is unlikely to affect their performance, but they are very attractive and a bit quirky.
Lastly we come to my favourite, bamboo needles. The higher quality polished ones can be a bit more expensive, but there are some cheaper ones available too. I find bamboo to be light and easy to use, and they are also very strong. They have good points on them which are quite resistant to wear. The polished ones are very good at allowing your yarn to run smoothly, and even the cheaper, less polished ones are still very smooth.
As I said at the beginning, deciding which needles are the best to use is eventually a matter of personal preference. I definitely recommend, though, that if you do a lot of knitting on a regular basis you give serious consideration to using bamboo needles. I find them a lot more comfortable to use, and am much less likely to have problems with my wrists when using bamboo.