Wondering if I could garner some advice about what key is most preferred for a flat set. I am thinking of trying to purchase a flat set, and notice that they come in several keys. I liked the sound of a Childress set I heard in B, but was thinking that Bflat might be better for playing with a Bflat flute, or with F whistles. Also, are all flat chanters narrow bore? Sorry for my ignorance. Any advice or info would be appreciated.
With the flat sets it’s a toss up for me between B and C, if I was to order a full set today I couldn’t tell ya for sure between those two keys the one I wanted, but this is just me; although I know if I had either one I’d sure as hell happy with it. 
And as far as I know, all flat sets are narrow-bored. However as I understand it, there are some D chanters which are narrow-bore as well.
I think you’ll find that this is extremely subjective. Everyone’s taste is different. Personally, my favorite is B. But, after hearing and playing a couple of very nice C# sets, I think I could easily enjoy having one of these. Each key has a different timbre and thus seems to fit differently in different situations. If I was independently wealthy, I’d get a B set and a C# set!
Amen brother. 
If I was independantly wealthy I would have a full set in every key 
Bb and B chanters sound lovely (even when I mangle a tune on them). C and C# I have to wait to comment untill Chris Bayley finishes my chanters 
David
One important consideration, apart from the sound, is what you plan to do with your pipes.
If you’re planning to play solo, and have no interest in playing with other musicians, then you can take your pick of the flat pitches. However, if you think you might want to play with other musicians, C is probably the best pitch to choose. B, Bb and C# are difficult pitches for other musicians to play, unless they can down-tune their instruments or use a cappo.
Another consideration for B and Bb is that they may not be true B or Bb in a scale where A=440 (although the set will be in tune with itself). Again this is not a problem if you’re planning to play solo, but it may cause problems with accompanying musicians.
Personally, I really like the sound of Bb pipes. One of these years I’ll get a Bb set.
Oh yes…my fellow Pipers,
When I get the money forward…(HA HA)
I’m getting a set made in Bb with 5 regulators, for the ultimate
Irish Pipe experience ! Brad Angus is in the midst of making
the 2nd of two such Pipes, for the “REIT-mann” !
I have to add… that the thumb and 3 finger “G” on a Bb set
is actually sounds an Eb.
Kevin’s remark to Wally Charm, about B sets being
“Way Too Shrill” as mentioned in other postings…
still makes me laugh !
Sean in Eb, D, & C Folsom