i have a Clarks, tweaked by Jerry Freeman, which keeps the slightly breathy sound associated with conical whistles..but it's a bit quiet for sessions (fine for amplified performance though).
It's great right through the range, and doesn't suck the breath out of you like the regular ones.Cost me £23 from Big whistles in Accrington, lancs.
My usual whistle though, which I use in performance and at sessions, is a Susato (plastic). Never had a problem, and it's tunable. Costs about £20 these days, I think.

Adh mór!
Dáithí