I have collected needles whenever I find a sale, and now I have enough to be able to knit anything. I like using dpns for socks, and for finishing hats, because I don't like Magic Loop.
I have fixed circulars in 16 inch lengths and 24 inch lengths. The 16" are for hats, and the 24" are for everything else. I also have a few 40 inch circulars for making very large items. Some of my needles are metal, and some are nylon. I don't like bamboo.
In addition, I have two sets of Denise Interchangeables, and one set of Boye interchangeables. But, I usually prefer using fixed circulars, so I don't have to worry about the cables coming loose from the needle points while I'm knitting.
My advice to you would be to try different kinds of needles with different kinds of yarn, and see which ones you like. It would be a pity if you spent a lot of money on needles that don't work for you. Good luck with your search!