I’m a rank beginner, and have been teaching myself via You Tube for a couple of months. I have three D whistles, a Generation, a Walton, and a Tony Dixon (which I love). I’m thinking of getting another whistle in another key, but the question is, which key? I’d appreciate some suggestions, with your reasoning included. Thanks in advance. Hopefully, in time, I’ll become a contributing member of the forum.
It’s hard to go wrong with a b flat generation. Great key for a whistle and the b flats are consistently pretty darn good. Could be hard to play with others but great by itself.
A C is a great key to play with others in. A minor tunes are fairly common at sessions and render on a C whistle well. For cheap Cs, I actually think the Waltons is ok. Don’t have a lot of experience though with cheap Cs.
An A whistle is good for all of those A tunes as is an E. If you finger an E whilst like you are playing in G on a D whistle it renders in A.
G is also a good key, you can play a minor tunes and G tunes with one.
Are you wanting to buy a whistle in another key to play tunes/songs in different keys or just for the different sound? If you want to play a particular tune or song then that I will help determine the key you would want to get. For example, I need a C whistle for a couple of the songs my band does, and I need a G whistle for playing with another singer.
I have a Bb generation, and it is a quality whistle for being untweaked. The Bb tone is also pretty great, and the stretch isn’t that far from a D or C whistle. Once you get to something like a G whistle, you have to start thinking about adjusting your grip on the whistle. The larger the whistle, the more useful a “pipers” grip is.
I’d third the Gen Bb recommendation.
As far as cheap C’s (another nice to key to have) go, Oaks are my personal favourite of the currently available mass produced brands.
If you are new to playing and wanting something for playing at the house, just choose the key that gives the pitch range you like. If you already own a D whistle then you have what you really need for playing Irish trad with others.
If you already own a D whistle then you have what you really need for playing Irish trad with others.
As long as the others are playing in D (and related keys) ofcourse and you’re handy enough at the half holing to get through tunes like The Humours of Scariff, The Porthole of the Kelp, The Tempest or The Boys of Malin when they come up.
As for which whistle to buy, you have to please yourself. Find one you like and that suits you. Buying someone else’s favourite whistle, you’re doing just that: buying someone else’s favourite whistle.
For example: I went for decades without the need for a Bflat whistle and only recently came into an old Generation Bflat, that came with batch of other whistles. It’s lovely. Still haven’t used or needed it since but I wouldn’t assume that will hold true for anyone else.
Thanks to all of you who responded. Lots to think about there.
All good suggestions above. And, welcome to the whistle forum.
Many thanks for the welcome and, once again, to everyone who responded.
Funny that so many recommend a Generation Bb. Just bought one of those yesterday and love it. Not really useful when playing with others though - except for clarinets and saxophones 
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One thing that hasn’t been mentioned - on a Tinwhistle it’s very easy to play two scales - 4 if you also count the corresponding minor scales.
So a whistle in A can very easily play in D when using this fingering: oxx ooo
You start at the D: xxx ooo then comes xxo ooo, xoo ooo, oxx ooo, xxx xxx (or: oxx xxx), xxx xxo, xxx xoo and finally you arrive at D again with xxx ooo.
Considering this I think besides D and C the two most useful are G and A, because then you can play in the following scales easily:
Whistle in D: D - G and minor: b - e
Whistle in C: C - F and minor: a - d
Whistle in A: A - D and minor: f# - b
Whistle in G: G - C and minor: e - a
And then get a Generation Bb for fun 
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That should cover 90% of the songs out there.
I’m hearing a couple of different themes:
(1) What do you NEED it for?
(2) What sound do you LIKE?
(3) I would add: Otherwise no need to do anything.
(4) I would add: I’m more likely to buy a different D-whistle because I want a different sound quality.
In typical sessions (around here), you only NEED a D whistle. There are a few tunes for which you would want a C whistle or else go order a beer. Recently, a new guy came in who plays a lot in A, so maybe I have a reason to get a different key whistle.
Here is an example of my decision process that would lead me to need a new whistle: I really like how Eileen Curran sounds in the high register: A-dorian on my D-whistle. Some fiddlers stick to first position, which makes the high C-nat a bit difficult for them, so I am negotiating which key would work best for us both. G-dorian? I need a C whistle. E-dor? I need an A-whistle, or play it in E-dor on my D whistle.
Or: The JB Reel sounds so much nicer in the low register, that for the first time, I’m almost tempted to get a low D-whistle… learning flute instead.
I was also once young and restless, and thought that maybe I needed a whistle in a different key… I bought a Bb Generation, and that was 40 years (geez!) ago. I can honestly say that I have never needed it, and in fact I never even played it. But recently, I decided that I quite liked its sound, and have started playing it. Of course, I don’t have anyone to play it with, so it is purely for my own pleasure.
I understand what you are saying, and I would agree… partially.
It turns out that there are very few tunes actually in the minor key. Usually these “minor” tunes are really in the Dorian mode.
But, to amplify your point, you can also play in the “relative” Myxolydian modes, D-Myx in key-of-G or A-Myx in key-of-D.
I think of the “circle of modal-fifths”:
Scale notes in the key of D give you:
→ D-major
→ count up five to A-Myxolidian
→ count five more to E-Dorian
→ count five more to B-Minor
That gives you eight “keys” on a D-whistle.
But, that’s not all!
Some tunes are Pentatonic or Hexatonic instead of Heptatonic,
So, you can play Farewell to Whalley Range (F#minor-pentatonic) easily on a D-whistle because you never actually play the A#'s.
Do we have to thank the pipers for this!?
A minor’s pretty easy on a D whistle too.
@tstermitz
You’re of course right about the additional modes. I didn’t include them as I’m not too familiar with the traditional Irish tunes, so I don’t really know which modes are most common. I have to admit I mainly play other music on my whistles. Yesterday I played together with my wife who plays accordeon and used whistles in C, D, Bb and G and could cover any scale she was playing in. The music she plays so far (she just started playing) is mainly C major but there were a few others. So I think with whistles in C, D, G, A and Bb you can play probably almost everything in popular music (outside traditional Irish music). It’s already established that for traditional music a D whistle is sufficient . For all other types of music I think the most useful besides a C whistle is one in G.