I’ve tested about ~20 whistle variations. Optimizing for blowing efficiency, filament usage efficiency, and dB output volume, the single color print of this one is the best I’ve seen so far: https://makerworld.com/en/models/2365496-minnesota-state-flag-whistle (based on https://makerworld.com/en/models/1642251-flat-signal-whistles)

If I’m ignoring filament usage efficiency, this one is much bigger and unmatched: https://makerworld.com/en/models/548070-triple-tone-extreme-whistle