Hm, interesting thread. To be quite honest, my least favorite keyed whistle, is D. Why? Tired of playing it in sessions and what not. When home by myself, I spend most of my whistle time playing C, B, or Eb every once in a while. I play uilleann pipes too, and although I love playing them more then anything else, D just isn’t the butter on my bread much these days… I’d love to have a C or B set if I could. I’m a mood player, so I tend to pick up whichever whistle I feel like at that given time-save for sessions of course, then it’s back to the workhorse of D major.
As far as musical Keys, go, hah, shouldn’t my profile name say it all. Neh… Although it is a bright key, I’d say maybe my next favorite key in Irish trad is possibly B minor… Sad, mad, it’s all bad, but who cares Mom, I love trad!