Which whistles have such a beautiful tone that playing them makes you very happy?
They aren’t just adequate tone, they sing, they speak to you, they pick you up, they bring summer to winter, they are refreshing!
I’ll play. I have 2. First is my freeman blackbird. That thing just sings, and I feel like it makes me sound better, too. I also have a Mack Hoover in A, and that whistle (just a tad lower and quieter) is like magic to play. Mellow and balanced.
My old Generation C whistle after I added some blu-tack on top of the ramp, slightly shortening the window. It killed the harshness that previously spoilt it, although I’d also liked it before as I didn’t know any better, but once you’ve heard what it can do, there’s no going back.
Before I experimented with that, I made a prototype whistle head for a quenilla (which I also made) and got such a good tone out of it that I stayed up three hours after I’d intended to go to bed just to go on playing it. Now though, the modified Generation whistle sounds practically as good for tone. The quenilla has a 15mm bore and a much stronger lower octave, while the second octave is only a little louder than the Generation until you get to high A (I checked with a sound meter app, making sure it was far enough away not to reach 90), although you do feel the need to blow harder. It doesn’t sound like a “traditional” whistle, seeming to be about half way between a Generation and a recorder, but it’s nice.
One I don’t own – McManus
One I do own – Woodi. Sample – https://folkfluteworld.com/reviews/review_of_woodi_tin_whistles/ode_to_woodi_in_c.mp3
Or maybe the first whistle I ever bought years ago, my old Clarke Sweetone.
My Burke composite high D has a gorgeous full voice with very little to no wind noise. It’s the whistle I chose to play for a friend’s wedding ceremony.
My Shultz PVC Water Weasel high D is a close second and has a spot on C natural when fingered OXX OOO.
Neither of these whistles is currently available on the retail market, but might be found second-hand.
There is indeed a Water Weasel currently on eBay:
My McManus. It was a gift from my fiancée, which already makes it special. But its tone is simply my favorite! I love how round and “wooden” it sounds.
Goldie is another favorite. Not quite as nice a tone, but it has beautiful, rich low notes like no other whistle I’ve played.
And for C, my Karavaev Nightengale. It’s got the sweetest, most balanced tone, and it always feels so effortless that it’s like it’s playing itself.
When I’m playing well, whatever I’ve got in my hand. It’ll be from a small range (a Mk 1 Feadog, a Killarney, and a O’Brien Rover), but it has included the sub-par Generation D that lives in the car.
Any of them could sound distinctly uninspiring the next day.
On a bad day I’ll be cursing their tendency to clog or sound shrieky on the top note or not be as responsive as I’d like, mostly because I know it’s me that’s the problem.
I’d say you’re lucky. I’d count that as a blessing most of the time. Although, to be fair, I do have the odd good day … 
My favorite at this stage is a Tony Dixon DX005. No tweaks or modifications. It has a beautiful, sweet, clear tone in all registers which it bridges effortlessly for me.