I am looking for a high C whistle and would like opinions on what brands you have and why you like it.
Tony Dixon tuneable aluminium, has a lovely tone, & I can play it as a high flute/piccolo too, because I bought the Duo model. 
I don’t have too many of these high C, but another I like is the Clarkes Sweetone, & I have a couple of Generations & a couple of plastic ones that also sound quite nice.
Hi Frizzygirl
My high C whistles are part of sets, a Syn D/C set, a Syn A to E set (one head and multiple bodies) and a C/B set based on a Sweetheart C whistle.
I like both the Syn and Sweetheart C they are not difficult to play and in the case of the Syns, incredibly robust. The Sweetheart, being wooden, would likely be a considered purchase. The Syn C is only available as part of a set of whistle bodies with one common head.
If you are in the US, then look at the Irish Flute Store. In the UK try Big Whistle.
David
My favorite and go-to C whistle is a 70’s-vintage Generation; nimble and light, good tone.
I also have a O’Brien wooden whistle that comes with different tube pieces to play in both D and C. I’m not crazy about wooden whistles, but this one plays in tune and is nice enough for what it is. The sound is quieter and more mellow than my Generation; sometimes I use it when playing with my wife to let her harp come through more.
The only Cs I play, listed alphabetically:
Freeman Blackbird
Shearwater Alloy
Susato Oriole
It’s hard to explain why but I’ll try.
Blackbird’s sweet voice and gentle air requirement.
Shearwater’s hiss and it allows me to lean into high notes without being screechy.
Susato’s volume without being obnoxious. I must say, though, this is the only Susato that I actually like.
All of them have a nice OXX OOO
The only C natural I have that is still purchasable is the Killarney nickel silver tube. I find it quite nice, even and easy to play, but don’t use Cs very much. I have an O’roirdan and a Schultz water weasel set that have Cs. Both of these are very nice but not easy to find.
Thank you all for your input. Much to consider! 
Just to add to the options, Jerry Freeman Mellow Dog C…
Best wishes.
Steve
Favorite : Feadog nickel. My wife bought it for me during a trip to Scotland a few years ago.
Second: Susato Kildare. Good volume. Excellent intonation.
Third: Parks walkabout. Great intonation. Controllable volume.
+1
I also love the Feadóg C. And my vintage Generation but the head cracked over the years. Still plays fine though. My first whistle.
I have a few inexpensive C whistles but my go-to is an older Generation that I got from the thrift store for $.99. It plays great and looks like it came out of a treasure chest.
If any of your playing will be outdoors, it’s hard to best the Susato Kildare. Very resistant to wind and, in my opinion, the best sounding key in the Susato line. I recommend the o-ring tweak that you will find discussed in older posts.
My #1 C whistle is a Generation I got around 1980.
I’ve tried C’s from Burke, Susato, Sindt, Dixon, and so many other makers I can’t remember, including fancy wood ones by big-name makers that cost several hundred dollars, and none of them come close to that Generation.
It’s had no modifications to the head other than filling the cavity below the windway, which raised the 2nd octave a bit, and sweetened the tone overall.
As it came, the “G” (in D-speak) was sharper than all the other notes, and I played this whistle for years with tape on that hole.
Then one day I bit the bullet and chopped the bottom and carved out the other holes to give a perfect scale with no tape.
A few months ago I bought a pile of old cheap whistles and the diamond in the rough was a Waltons C that is superb. It’s probably the second-best C I’ve played.
As far as the “why”, what I like is a very sweet easy light responsive 2nd octave and a full round low octave, with minimal “break” between the octaves, and a complex sophisticated tone.
Like Big Davy I am also a fan of the Syn C. You can buy it on the Oz Whistle site or direct from the maker Erle Bartlett. Mitch, on the Oz Whistle site, describes the Syn C as “pure magic” and I think he is correct. You can buy it as part of a D, C package although I wouldn’t let that put you of because if you buy the D the C tube is only around (at least last time I looked) $20 AUD and if you are an overseas buyer $110 AUD for the set must be extraordinarily good value.
BTW I notice that Mitch had a once off West Indian Cocus Wood high D for sale that went really quickly. Missed it when it came up or I might have bought it. Did anyone here buy it if so what’s it like?
All the Best
JT
This one for me too.
I’m not sure you would see THAT much difference between the D and the C of any maker… if you like their D, you would probably like their C, no?
Anyway, I have a Generation that’s pretty good, but my main C is a Humphrey. I bought a D+ (seven holes), and a C tube fits that head so I got the C tube as well. I mostly leave it set up as a C. I didn’t like the D+ as much as I thought I would (nothing to do with how Gary made it, just didn’t use the extra hole much and found it distracting). Anyway, it’s a very nice whistle.
if you like their D, you would probably like their C, no?
Well, in short : no. There absolutely no guarantee a maker will arrive at the same, or even similar, voicing/playing characteristics at all.
I have Sindts in D, Bb, and A. There are SMALL differences between them, maybe, but they are all closer to each other than any of them is to any other whistle I own. That’s a small sample, I’ll grant you, but other than my Humphrey set I don’t have multiple whistles by one maker to refer to. But based on MY three Sindts, I would be very surprised if I order a C or an Eb or whatever and didn’t like what I ended up with.
Olivier Bouchard makes the best C whistle I’ve played . Box wood and brass, slightly wider bore . Get one!! Brilliant
I’ve played a Chieftain C tuneable for the past several years. I own other high end whistles in C, but find that the most expressive and excellent playing of my horde is the Chieftain C. Countless C&F threads have discussed that Chieftains can be variable from whistle to whistle. This may be true, but not my experience. The C whistle is a gem, and when I play it, I often get comments and praises from other whistlers, and listeners. (No eviction notices or complaining canines, yet). I’ve used it as an instrument for dance improv and other such strange solo gigs. I highly recommend them, and, also, for a more bird-like tone, any of Mitch Smith’s OZ whistles, in D or C, as they are simply the absolute best and most consistently pure sounding whistles of the craft.
If you’re interested, look into Kerrywhistles.com, or OZwhistles.com
(The other whistle in the pic is a Kerry Songbird D - sadly, no longer in production, but a brilliant D) (Case by Martin - Just Stow it)
Also, I once recorded a TV soundtrack using a borrowed, pre-air dam, Copeland brass C whistle, (which is high on my coveted whistle list), but it seems they are nowhere to be found, except, maybe, for the few that still exist in collectors drawers and attics. If you have one of these, drop me a line.