I prefer public critiques. This is supposedly an art site. If art critique doesn't belong here, I don't know what does.

If it's out in the open, everyone can read it, including others that might benefit from the advice. It can also be a "reality check" on the critique. Others can offer their own takes, whether supporting the criticism or supporting the work as it stands. (My personal rule of thumb: If one person doesn't like it, well, that's just one opinion. If two people don't like it, it could be just a fluke. If three people don't like it, change it immediately. ;-)