I’ve been thinking I would like to play tunes in the key of A. I’m thinking that a whistle in E would be perfect for this because most tunes I know are just right for a D whistle except for the pesky G# issue. So an E whistle would solve that problem, plus I’d get a few notes below the tonic.
Do you agree? Do you think an A or an E whistle would be better?
Do you think anyone would trade an E whistle for a few Generation whistles (Eb, C and Bb)?
Maybe you go for an A with a flatted 7th thumbhole.
Yes. 
For most Irish dance music in A major, the E whistle is the one that gives you the right range or tessitura. An A whistle will have you folding octaves like crazy.
I do consider it a cheat. There’s no reason not to play A tunes on a D whistle. The G#s are both there.
But I carry a Susato E for playing A tunes in G fingering. Sometimes I cheat. 
Surely it depends on the tune, and the context. Plenty of A major tunes can be played on a D, but if they sound better on an E, why not? Other tunes might go down to D, and thus be unplayable on an E anyway - just as ‘Dark Island’, in G, is played on the C whistle because the tune goes down to C.
If you’re playing a set of tunes for dancing, then the keys of the other tunes might make the decision for you, if you prefer to avoid swapping whistles in mid-set.
So logically, if you learn a new tune in A, you’d want to be able to play it on E and D whistles, if possible.
WhOA dictates that you should get both. 
Thank you everyone for the responses. When you said that A tunes sound good on an E whistle it reminded me how A tunes sound really good on a cross-tuned fiddle. I wonder if there’s a similar effect. Probably not.
Unfortunately (or fortunately) I do not have whoa. I have too many whistles and would like to eliminate a few. None of them are anything special, though. I like cheapies. So I have to figure out how to get an E whistle and get rid of at least 2 or three current whistles in the process.
I just feel so frustrated with my flute not being able to play A tunes very easily and really hate it when you have to fold octaves. So it sounds like E is the ticket.
Looks like only Shaw makes them. Is that so? I don’t suppose an Eb whistle could be tweaked? Nevermind. I’m worthless with my hands.
Dr. Colin Goldie, PhD, MD. makes wonderful E whistles. And they are strong players also. Swami Govinda Mahatma Lama Carlos