My Pear Drop Shawl with my Size 4 32"Signature needles. Having good needles is making this project so much more enjoyable.
Good needles are probably the most importnat. The needles you use can make a project the most miserable experience ever if you get the wrong ones. For example, if you're knitting with a fiber that is really "grabby" like mohair and you are using bamboo needles you are probably going to want to stab your eyes out. The fiber, by its nature wants to stick to things and bamboo needles are "rougher" than others meaning there will be a lot of friction between you yarn and needles and you will be pulling against this friction with every stitch. Conversely, if you're using 100% silk or bamboo or some other very "slippery" fiber you will probably love bamboo needles because the bamboo will "grab" the slippery fiber and keep it from slipping right off your needles. (I have a silk-rayon shawl that I started on metal needles but it kept sliding right off the needles if I picked them up vertically. After loosing all my stitches twice because of this, I wised up and switched to wooden needles and haven't had the problem since.)
Aside from choosing the right type of needle for your fiber, you should think about the type of project you will be working on. For example, cables put a lot of tension on your wrists to make because you have to leverage the stitches around one another. Also, because they are twisted, cable stitches are tighter and harder to get your knitting needles into than "normal" stitches. If you are a tight knitter to begin with, you might find that you break wooden needles when knitting cables. On the other hand, if you aren't too tight of a knitter, you might prefer wooden needles because they have a bit more give (the needle is literally more flexible) than metal needles and therefore the needle absorbes some of the tension from the twisted stitches and keeps it from transferring to you wrists. I prefer acrylic tip needles for cables because the acrylic is flexible like wood, but the needle point is often sharper than wooden-pointed needles making it easier to "dig" the needle into the tight cale stitches.
The last thing that is very important to consider is the sharpness of the needle tip. Sharp tips are absolutely essential for lace knitting. When you knit lace, you are manipulating tiny tiny yarn in lots of ways. Often there are many increases and decreases every round. It can be nearly impossible to get a blunt needle to "k5tog tbl" With a sharp needle you have half a chance of actually enjoying the nupp-making experience. Blunt needles also have their place. If you are having problems because you a knitting with a yarn that is "splitty"--i.e. you keep knitting through the plies of the yarn rather than around the yarn strand--try working with a blunter needle. A sharp needle can slice right through the plies and actually makes it more likely you will split your stitches if you are knitting fast. A blunt needle can't penetrate the plies and is more likely to slip around the yarn strand like it is supposed to.
Some people think it's a bit excessive when I mention that I have 4 complete interchangeable needle sets, (as well as many other non-interchangeable needles) but I like to think that I just have the right tools to execute my craft in the best way possible. I don't just need "a size 6 needle." I need a size six needle that is: wood, metal, acrylic, sharp, blunt, long, short, etc.
Do you have a huge knitting needle collection? Only a few? An interchangeable set? Two? Four? Do you only buy needles when you decide to do a project that calls for them? Are there sizes you don't own? Sizes you own more than 6 of? I'm curious.