Just wondering. Also, just to prevent confusion, I want to know the most popular, not your opinion!
…
Although an opinion would be nice =P
While I’m at it, how’s the Overton high D?
Cheers,
Armand
Most popular as in played by more players than anyone else, would at this point probably be either Generation or Susato.
Not too many C&Fers play Overton high whistles, although a few do.
My favorite high whistle is Feadog, FWIW.
My first whistle (which I purchased about a year ago) was an Overton High D by Colin Goldie. I purchased it after listening to many sound clips and falling for the “cosmic drainpipe” sound. I was a bit leery of the backpressure and tendency to clog that I had read about but have come to appreciate the backpressure and learned that having a little patience while the whistle warms up is well worth achieving the sound that it produces.
The most popular whistles on this board may be Michael Burke’s and for good reason; Mike makes wonderful whistles. Mike’s most popular seem to be his brass whistles, but my favorites are his composites.
Feadog? I would have sworn you were married to your Humphrey whistles. 
But I like Feadogs, too. Not sure I really have a single favorite high whistle, though - depending on my mood I might pick Syn, or Serpent Sweet Polly, or Oak, or several others (including my clear “mystery whistle”).
I have probably had the best luck (among inexpensive whistles) with stock Feadogs and Clarke Sweetones, though.
You guys are circumventing the question. Wouldn’t it be a Gen. or a Clarke original, just based on volume sold?
Hi:
My favorite is my Chris Abell in blackwood and sterling.
Debbie
I think the best are the custom made one of a kind whistles
Your point is a good one, emmline, and your answer may be what Armand is asking for, but I wonder if more Generations are sold because they are more popular (widely liked or appreciated) than many other whistles or simply because they are more affordable.
Well, there is that, of course. 
But I like Feadogs, too. Not sure I really have a single favorite high whistle, though - depending on my mood I might pick Syn, or Serpent Sweet Polly, or Oak, or several others (including my clear “mystery whistle”).
Yeah, those mystery whistles are nice, aren’t they? I hear Redwolf likes hers, too.
Trying to be on-topic, no. Are we talking cumulative (sales over time) or current sales?
If current sales, I think that Generations and Clarke Sweetones are probably the hands-down winners. If I can find tinwhistles in a local music store (non-IRTrad specialist) it will usually be one of these (or, occasionally, a Clarke original model).
The Sweetone sound isn’t my favorite, but they’re quite decent whistles (and usually quite playable out of the box). I like the sound of a good Generation, but there’s much higher chance of needing to tweak it a bit.
But there are a LOT of good whistles out there for less than $10.
Does sheer sales volume make a particular product the most favorite or just the most sold? Considering some have claimed to buy Gens by the box or case to find just that SPECIAL ONE, or the number that must tweak them to make them truely playable I really wonder about that.
There are many whistles that are extremely popular but due to cost (Copeland and others) or availability (O’Riordan comes to mind) sales may not match those of the “cheapies.”