Having lost two metal whistles which unscrewed, and finding my clicker whistle a bit bulky, I bought myself a nice purple Acme 210.5 (with lanyard) on the recommendation of several people here, and I love it! I confess to having bought myself a green one as well, so that I can choose which colour goes best with what I am wearing!
I'm buying my daughter her own one for Christmas (probably a blue one) - it will make a nice tree present!