I completely agree with everyone...you'll need them all. In fact, if you're like me, you'll need duplicates of all the sizes, so that you can knit two things at the same time (2 socks, 2 sleeves, etc.).
I've learned both the Magic Loop and knitting with 2 circulars, but I still love knitting with DPNs the best.
Save yourself the time and aggravation...buy the entire set now. :roflhard: