There are many types of knitting needles, straight and circular, aluminum, bamboo, short, long, wood, nickel plated, expensive and inexpensive. Although you can use any type of needle with any material some needles and materials work better than other combinations. As a fiber, wool is the most forgiving and can be paired with any type needle, but other fibers work best with a specific type of needle.
A knitter will favor a certain type of needle because of personal taste and comfort, but here are some other things to consider. Bamboo or other wood needles are suited to slippery yarn because the yarn is less likely to slip off the needles inadvertently. Examples of slippery yarns are silk, rayon and microfiber. The yarn does not stick to itself like wool does. One way to tell if a yarn is slippery is to look at the skein of yarn, if the yarn is constantly falling off the skein that is an indication it is slippery. Plastic needles are also less slippery than metal needles.
For working lace, needles with sharper tips work best. Lace yarns are so fine that sharp tip needles, such as Addi-turbo lace needles, slip under the lace strand easily. Cotton often splits when using needles with sharp tips though. The sharp tip does not grab the whole strand and instead pokes through and grabs just part of the strand therefore when working with cotton a blunter tip works better.
When deciding between circular or flat needles the size and type of project is important. If you are working on a fair-isle sweater circular needles work best, but circular projects such as socks can be knit on two circulars or double pointed straight needles. The pros and cons of each often come down to personal taste and habits. When I first started knitting socks I used four long double pointed straight needles. I mostly used sock weight or fingering yarn and American size four needles. I then switched to four short double pointed straight needles, which made my knitting go faster and more smoothly, but when I packed up the sock the stitches often fell off the ends. I am now a fan of using two 16 inch circular needles, they make my portable sock projects more portable and I rarely lose stitches off the ends. Whether you use 7 inch long double pointed needles or 4 inch long double pointed needles is often about which feels more comfortable to you. I found the longer needles harder to work with because the ends caught on the yarn and my sleeves. The shorter double pointed needles were much easier for me to work with, but I did have the problem with the yarn falling off the ends.
If you are working with a large project, circular needles are often your only choice because the project wonít fit onto straight needles. The most common complaint about circular needles is the join between the actual needle and the wire connecting each end. If the join is not smooth the yarn catches on the join, and that makes the yarn fray or ruins the rhythm you are sustaining. When knitting and going at a nice steady pace stopping because your yarn is stuck it is very annoying. Most modern circular needles have smooth joins, but it is something to look for when selecting needles.
A final reason for choosing one type of needle over another is price. Needles cost many different prices, straight plastic needles cost much less than nickel-plated circulars, but the knitter must ultimately decide which type of needle they like working with best. If your tools donít suit you I suggest going to your local yarn shop and sitting with some yarn and a variety of needles and seeing which you enjoy working with best. Knitting should ultimately be a pleasure and a project takes many hours, months or even years, so choose your materials so that your enjoyment of this craft is heightened.