I always use the strip method (starting with the mouth then noise then eyes) and it works well with good ref. box model i find you spend alot of time fighting to lose the shape of the box. I never have and never will try and make one from sphere. Although i do tend to place 3 in the scene to build around (eyes and back of head).
I have been making heads so long I can pop one out in a few hours now - minus the ear and hair. I must stress the ref part again - trying to fudge it will slow you right done as you'll keep looking at it and thinking that dont look right. I know some people who spent time getting a good head togeather and then just tweak it for then they want a different head. So there are ways of doing heads quickly but it takes some work to get there.

Good luck but most of all have fun with it.