I really think that any good whistle will get you well started. And sticking to one until you’ve mastered the basics is a good idea. Until you can control one whistle well, switching to another whistle is more a distraction than a help.
The trick is getting a good whistle - though not as many as beginners may think, a real dud may put you off whistling.
The thing is that it’s hard for a beginner to distinguish between a good whistle and a bad - starting out, it’s all to easy to blame your own lapses on the instrument. (I have several Generations and Feadogs that have mysteriously improved from “dud” to “really nice whistle” over the time that I’ve owned them). But I also have a Walton’s D, my first whistle, that really is pretty bad. Just unplayable when I started out, barely playable now - fortunately, the Feadogs I bought a few days later were good whistles, and got me over the hump.
If you’ve got a decent whistler who can test-play your whistle, you’re all set. If they can sound good on it, so can you if you work on it. If not - well, I’ve had good luck with Feadogs, Walton’s C and Mello D models, and Clarke D Sweetones (C Sweetones sound OK, but I don’t like the long reach for the bottom hole). I like Dixons, too. I also like Susatos and Oaks, but they do need a bit more breath control.
What would I give a beginner? Two whistles - a Sweetone and a Feadog, both in D. Both are inexpensive (the two together would be $10-12 dollars), both are pretty consistantly good, and they sound quite different.
And tell them that though they will probably end up buying lots more whistles (WhOA is me!), those two whistles could easily be the only ones they’d need for years to come.
I’ve seen some pretty fine whistlers - all far better than I - who either stick to the cheapies exclusively or give them equal time with the handmade models. The high-end models are nice, but many of the best are designed to sound like a “good” cheapie. And once you’ve got the basics down, most cheapies sound pretty darn good, too.