I would define "best" as the the limit of this calculation as the sample
rate approaches infinity:
rise/run between each adjacent data point of instantaneous phase
I could simply bump my sample rate up very high, but there would be
advantages to having a function instead of having to numerically calculate
the rise/run between each adjacent data point. Having a formula would make
implementing this calculation in certain environments other than Scilab or
Matlab possible/practical, such as in VST or Reaktor.
Thanks again for setting me straight earlier Dale. Were it not for that,
I may have gone on thinking that the rate of change of phase was constant,
and not calculated its rise/run. When I saw that plot of approximate
instantaneous frequency I really jumped with joy, it was exactly the type
of thing I was hoping to find.