When it comes to material that part is pretty simple. There's really two things to consider there:
1.) Weight - metals tend to be heavier than the traditional bamboo.
2.) Drag - meaning does the yarn move quickly over the needle or does the needle's material cause friction as it passes along the shaft thereby slowing down the movement of the yarn.
As a general rule of thumb, metals tend to not have much drag. Therefore your yarn move over them much quicker. This is great when you are like me and like to knit quickly. It's not so great if you can't control what's going on so well. Woods, i.e. bamboo, tend to have some drag to them. This can be a good thing. Since it slows down the movement of the yarn along the shaft you decrease the chance of the next stitch jumping off the tip of your needle. Thus resulting in your making a mad dash to try and grab it before it ladders it's way down your work. Plastics are the other type of material that you can come across. They tend to have drag as well and if they're poorly constructed can snag your yarn unpleasantly. Personally, if I see plastic I skip right over that needle and move on.
As far as weight goes, plastic tends to be quite light but as I said earlier not really worth it. Bamboo needles are a comfortable weight but you do have that trade off that you lose some speed. I should mention if you see that the bamboo needle is "carbonized" make sure you check how the yarn moves. Carbonized needles tend to have a lot more drag because of the process they go through. For the bamboo needles I have; I prefer the natural bamboo needles that are that lovely light tan color. If you're in a Local Yarn Shop, don't be afraid to ask if they have a set that you can try out. Lastly, we have metals. The type of metal can make a difference as well as manufacturer. Best advice I can give here is to again try them out. If you pick them up and right away think "Wow, these are heavy." You most likely will find them not so great to work with. I have some nickle plated needles nice, fairly light and the yarn just moves right along on them. I also have my personal favorites the HiyaHiya Sharps. They are stainless steel, incredibly light and super fast making them ideal for my personal preferences.
As far as the type of needle you need you really need to consider the project you are looking to make. I find that if it can be done on a straight needle I can do it on a circular set of needles so I don't bother with straight needles. If the project requires you to use circular needles you CAN NOT use straight needles so again, why am I bothering with having straight needles if they aren't multipurpose? I'm sure by now you're seeing that I'm a fan of circular needles. Even with my love of them there are times when they don't fit the bill 100% of the time. When that's the case we move onto our double pointed needles (DPN). If you're like me when you first saw them you thought "OOOO pick up sticks!" DPNs allow you to span spaces in circular knitting that are just too small for your circulars to go such as the crest of a cap or fingers on glove or some points in making socks. DPN's and circular both allow you to knit flat or in the round. The difference between them is circulars can go into the bigger places where DPNs can't and DPNs can go to the tiny places where the circulars can't. There is a helping hand relationship between the two in my view.
Lastly, a note on circular needles... they come in different cord lengths so make sure you take into account the project you are making if you are buying ones that are a fixed length. I just buy interchangeable circulars and then I only had to purchase the appropriate length cords as the extra which was a lot cheaper than buying multiple sets of circulars in varying lengths. This in turn gave me more money to spend on yarn!! Let's face it we can never have a big enough stash of yarn!
