I'm a bit of a use-the-best-tools-for-the-job junkie. I've inherited this trait from my Dad (who's a trained tool-maker and engineer) - my Mum will probably be nodding in recognition around now. I'm happy to improvise and make do for a while, but once I know that something is for me and I'm going to stick with it, I like to make a bit of an investment in the right tools.
This has happened recently with knitting. I've been knitting regularly for the last 6 years and over that time my needle preference has evolved. I started out with 14 inch straight inox needles inherited from my grandmother, and added a few pairs of wooden ones in sizes that I didn't have. I moved on to socks and used inox DPNs from Gran's needle box (these are still my favourite sock needles). For small circumferences and especially socks, I now know that I'm going to stick with DPNs so have added more sizes (inox for small gauges and wooden for larger). I can do small projects on two circular needles, but don't really like it.
Since I started knitting lace a couple of years back, I've acquired a few sets of Addi circular needles and like them immensly. Over time, I've found that I actually prefer circular needles to straights for all projects because the weight of the project always sits in the middle and not out at the end of one needle. Once I'd acknowledged that I hadn't actually used a set of long straights for well over a year, I decided to make an investment in good circular needles. I had a decision, either two pairs of the longest Addis in each size that I used (so I wasn't hampered by cable lengths) or a set of interchangables.
I went for the interchangables. Get Knitted were offering a starter set of KnitPro interchangables with three sets of points, three cables in different lengths, and some other necessary accessories. I'd heard excellent reports of the KnitPro needles and liked that there were nickel, wooden and acrylic points available that would all fit the same cables, so in I jumped (with a few extras - more points in the sizes I use most, and some markers and cable connecter so I can make really long cables eg for edging a blanket).
I love them. They make it really easy to change needle size and I can connect an extra cable if I need to try something on, rather than slipping the stitches onto waste yarn and then back onto the needle. They've also worked out much less expensive than the equivalent combinations of fixed circular needles (I've got the equivalent of 21 sets of circulars for the price of around 4 sets) and are really good quality. My long straight needles have gone into a box at the bottom of my stash and I'm not really sure that they'll see the light of day again...