I think it just has a lot to do with your choice of yarns and preferences for wood, plastic or metal. I have a set of plastic interchangeable and I use them mostly when I travel. That way if I see something in a yarn shop and I want to begin a project, I have a set of needles with me that are probably the size I need. I think if you have a type of needle you mostly knit with, then buy that type, ie. wood.
Good luck! I do like my addi circs, but have never tried the interchangeable addis.