I've been asked over and over, what my favorite cast on is? It's the Cable Stitch C/O http://www.knitting.about.com/od/learntoknit/ss/cable_cast_on.htm
Click on the link and you can see picture by picture instruction for this very simple cast on.
Q: Why do you like this cast on?
A: I never will run short of yarn as when using two strands.
Q: Is this the cast on you teach beginners?
A: Most defiantly! When a beginner learns this cast on it is very easy for them to see the forming of the stitch. Therefore, knitting into a stitch is a natural progression forward, from a beginners point of view.