Glock-A-Roo, those are some interesting tests and some of the methodology is interesting too.
The actual dB rating (which manufacturers state) will be measured in a LAB with perfect conditions and probably using a source of compressed, dry air, so its not surprising that results will vary.
Montanero,
For field testing, having two (or more) people test each whistle, giving three blasts, three three times would give a good average sound.
The ease of use is important for a main whistle, but I think that - for me - I'm willing to compromise on some features because my principal criteria is the ability to fit in my wallet. But its still a consideration.
Afterall the Best Whistle is the one which you actually have with you when you need it.
Some additional tests could be to measure the sound over distance, perhaps from the other side of a bush to try and gauge how the pitch travels (I would expect the multi-pitch whistles to fair best).
And remember to wear hearing protection too, those whistles are LOUD.