CLSG or NLCS???Watch
I know girls/have family who have gone to both schools.
I have only heard good things about City Girls School from girls and everyone I know who goes there is really lovely. However, transport is generally a bit of a pain (most people have to get the tube) so unless your parents can drive you in that's worth considering. Less space in the city but they still have a dance studio/climbing wall and a (slightly smaller) pitch and courts.
NLCS is better if you're thinking about US universities. It also has IMO more beautiful grounds, and a lot more space for sports fields. I knew one girl who was very unhappy there and moved, but several who were happy.
Both are really supportive when applying to unis and they seem about the same in term of pastoral care, so like most British schools happy to talk about pastoral care to parents, but not so great when girls actually have bad mental health. I know City has a counsellor though, I don't know about NLCS (it's apparently a little sink or swim).
I'd say to pick the one that felt more right for you at open days and they're both really good schools, well done for getting in!
I was at City for 7 years (left in 2019) and I had a sister at NLCS who left for sixth form (she wasn't massively keen on the school). I would say both schools have their individual benefits: NLCS has much more space and is better equipped in terms of drama, music, sports etc, and the vibe is much more what you would expect of a leafy private school. City is arguably more grounded, and the urban environment can be very beneficial to the right person - I enjoyed the daily commute and being able to meet up with friends from all round London, it has a much more independent feel than NLCS, which (according to my sister) can feel somewhat like a boarding school. Pastoral support at city is excellent due to the small class sizes and excellent teachers - they were very supportive of me during my time there and I know they have been for many others. Pastoral support at NLCS (although this is going back 5 years now) seems to not be great - however, they do have better facilities and provide lots of opportunities for students, especially help with US universities. I would also say that City is more diverse than NLCS in that they provide a lot of bursaries, which means there is much more of a social mix and it feels a bit less like you're stuck in the North London bubble. Overall, both schools are academically very strong but have a different ethos - go for whichever school you preferred the feel of and seems to be right for you! Hope all goes well and you reach a decision