Perhaps you just haven’t found your C-legs yet.
I only have one C whistle, but it’s a Copeland and I have nothing bad to say about it. I would like to get another C at some point, perhaps a wooden one for that wood-C tone.
…okay, I’ve fulfilled my pun quota for the day.
I’m quite fond of my Burke brass wide-bore C.
Update:
I am now the owner of a Jerry Freeman Tweaked Blackbird C. I’ve only had it a little over 24 hours but I really like it already. It has the sound I was looking for, and is very easy to play.
Now I’m eager to get back home and play it some more. 
Sarah
Just to let you know, in case you didn’t already …
The C Blackbird and the C Mellow Dog are the same whistle, except the C Blackbird has a black whistlehead and a nickel plated tube whilst the C Mellow Dog comes with a green whistlehead and a brass tube. (And the C Mellow Dog isn’t sold separately unless you make a fuss. The C Mellow Dog is part of the Mellow Dog D/C set.)
Best wishes
Jerry
I’m preferring the C and Bb these days, since they seem inherently a bit quieter than the D. I love my Freeman tweaked mellow dog C (the D’s nice too–great set). Really a nice value, and a mellow sounding (who coulda guessed, with a name like that?), very responsive brass tubed whistle. Some of the others mentioned I like too (eg Parkes with the two bodies). The Ellis C/D set is a good value, a bit pricier than Mr. Freeman’s, but with a “silencer” (or a “quieter”?..)
I have to say that, on the wood side, I have an Oz C blackwood that’s a dream to play. Quite a bit more dough, though, of course…don’t tell my wife…
Best,
Jaydoc