I have individual interchangeables that I really like. I have Cubics, Novas, and my favorites, Karbonz. The interchangeable tips from Knit Picks and Knitter's Pride are all interchangeable although the companies tell you that they don't guarantee their needles if you mix them with the other company's needles, but I've never had a problem.
I choose which needles to use according to the fiber content. Slippier yarns do better with wood and bamboo, or sometimes plastic. Yarns that are less slippery do better with the Novas, which are all metal. The Karbonz are nice for the acrylic yarns I use for children's hats that I knit and sell.
I like the shorter tips (or special tips) that allow you to put together a 16" needle if you use a shorter cord.
I like the Chiagoo interchangeable needles. Since I received my complete set of 5" steel, I'm looking forward to getting the mini's set (sock sizes) in 5" as well. I would love to get the bamboo (spin) complete set as well for those very slippery yarns. I love the fixed circular needles Chiagoo produces too. I started with those, then found I liked them so much got an interchangeable set.
You could say I love Chiagoo, which I use almost exclusively now.
I like circulars. I have Symphonie, Karbonz and Zing from Knit Picks, I don't like Karbonz because of the small gap between the tip and the body of the needle. I took knitting socks two-at-a-time (I tend to loose DPN's and never knit the second sock otherwise) and for that I've tried Addis and Chiaogoo, and I tend to preffer Chiaogoos.