This is like trying to get consensus on the best flavor of ice cream. Obviously we’re all going to have different preferences; however, anyone that chooses anything other than pistachio is daft, imo.
Get it? 
That said… I have no idea what whistles you’re playing, but if you’re playing on cheap whistles I think there’s a ceiling as to how good you can make them sound barring very rare exceptions. In high D, I own a mixture of cheap and high-end. On the low side, I have a Freeman-tweaked Clarke Sweetone, a Generation high D, a Walton Little Black Whistle, and a Walton Mellow Dog (the last three all self-tweaked). With the exception of the Sweetone which is the chiffiest whistle I own, the rest are all pretty shrill when compared to my high end Ds: an aluminum Burke, a nickel Copeland, and a gidgee Oz. All of the high end whistles are beautifully melodic and not at all shrill. In the end, whistles are probably like most other things in life in that you get what you pay for.
And before folks chime in about [insert name of well known whistler here] who plays a [insert name of cheap whistle here], let’s remember that whistles that we hear at live shows and on cds aren’t the actual sound of the whistle at all as they’re run through various electronic devices (mics, preamps, eqs, compressors, etc.) before the sound hits our ears. And I’d bet good money that [insert name of well known whistler here] who plays a [insert name of cheap whistle here] tested a box full of those whistles before finding one that was suitable.
I think I’ve said this here before, but my advice to people who are looking for advice on buying their first guitar (my main instrument) is to buy as much guitar as you can afford because the better sounding the instrument is, the more likely you’re going to play it and stick with it. It’s not an exact science, but there is a correlation between price and quality. I’d probably give the same advice to those wanting to learn the whistle. I know in my own case, my playing time increased tremendously when I bought the Oz, my first high end whistle in any key. A good instrument can provide great inspiration.
I realize that not everyone is going to be able to lay out $350 for a whistle, but a person can find nice used whistles at great prices occasionally if they’re diligent and keep looking. Just as an example, I recall there was a Copeland D on the used instrument board here that sold for $100 recently. That’s a steal and it’s not the first time such a thing has happened. And if the person is set on buying an unused whistle, there are good makers out there (some even on this board) that make very nice non-shrill whistles, some quite a bit less than $100. I’m sure there’s a thread somewhere that offers a list. But keep your eyes open, check the used listings often (bargains go quickly), and you’ll find a 12" hunk of metal or wood that will make your heart sing.