These equations are all approximations, and for some are all wrong. My max is at least 180 based on what we saw at my LT test, and I'm 55, 180#, and male. But they are all good for getting started.
Measuring max HR is of course more accurate, but is it really needed? Joe Friel has one setting up zones based on measured value of lactate threshold. Knowing this, why would I ever use a max HR equation?