Ok, here is a bit more about why I feel Channing suits us very well. It is quite an academic school but not as much so as NLCS or CLSG and it is not very pushy. I have a strong feeling that they think that it is girls who are happy work to their best standards, not necessarily those who are pushed. This suits some girls such as my daughter (who is quite bright but not at all competitive and who gets stressed under pressure) very well. The girls all seem very nice and even though there are differences between them, of course, and friendship groups within each form, the form as a whole seems to get on well, as evidenced by the continued existence of whole-form parties - which seems to be driven by the wishes of the girls, not the parents or teachers.
I do know of other girls who love it at City - which would not suit my DD at all. Slightly strangely, I felt a little uncomfortable about SHHS but I couldn't tell you why and my DH really liked it.
I have the impression that F. Holland is a little less academic than Channing but still very good and, in terms of its ethos, quite similar. It does have a more cramped feel about its premises but we would have been happy to take a place there.
Queens is much less academic than Channing and I think more liberal in its approach though the new headmistress may tighten things up.
One thing I can say for sure is that your DD will not suit all of these schools. If she is a City girl, she won't be a Queens girl and vv, IMO. Highgate and Channing are two very different animals.
The best recommendation I can give you is to go round these schools and look carefully at the girls you see and imagine your DD as one of them. Would she be happy there? Did you come out of the school feeling that you really enjoyed the visit or did it feel like a chore, or like an imposing environment? Could you see yourself talking to the headmistress about any issue that may crop up? Do talk to other parents with girls in the particular school you are interested in but do bear in mind that their girls may be different to yours. And do follow your gut instinct.
If you have specific questions about Channing, feel free to PM me. Hope this helps a little!