Tau is better than pi because a lot of useful expressions have 2pi as a term; SI is better than imperial because we happen to have ten fingers. Tau is a universal simplification like Planck units; SI is merely an anthropocentric simplification.
I think the greatest advantage of the SI system is that it's exponential. I don't care that much about what base is used, but switching is just confusing (12" = 1', 3' = 1yd).
Pi is better then tau because all of our damned engineering formulas have pi. SI is, however, the right answer (though useless without reference tools, whereas imperial isn't).
