Well some people would think being in the CSG catchment is the equivalent of winning the lottery. Whereas others (including us) have gone for the other local options despite being in the Camden catchment. So it's definitely a horses for courses thing...
CSG is obv good academically, particularly if you want Latin and Greek, or music.
It has a very cramped site, sandwiched between a main road and petrol station, and a railway line. It's very 6th form heavy, and takes in a lot of private school kids (including boys) at 16+, so that will affect the vibe.
Otherwise, and this is anecdote not data, it's quite a 'cool girls' school (which was one of our reasons for not choosing it). I have heard (again, anecdote) stories of girls instagramming pictures of self-harm, that kind of thing. There is also (again, anecdote) a bit of a divide between the middle-class girls and the girls from the local estates (they have a banding system, so different catchment areas for different ability bands).
If you're in catchment for CSG, then you're almost certainly also in catchment for Parliament Hill and Acland Burghley, so go check them out and see what you think. They both have v different vibes: Burghley is mixed and quite 'urban', but increasingly v popular - I really like the head. Parli has the lovely site on the edge of the Heath - building works atm, but that should be over within a year or so.
Don't be bamboozled by the difference in headline league-table results, as the schools have very different intakes (and as pp points out, Camden has an element of covert selection via the music places and via people gaming the system by means of creative address management.
I would say Parli parents are the ones who are too chilled for that kind of carry-on, and I know several families who have chosen Parli over CSG, including ones who have an older dd at Camden, make of that what you will. Parli has vg pastoral care, fabulously enthusiastic teachers and a good mix of kids - it's like CSG minus the hype, and with more green space.
But obviously other people think Camden is the answer to their prayers and the only state school they could possibly consider, so...
Really the only answer is to go to the various open events and see what you think - the three schools are very different from one another both in terms of physical space and in terms of pupils and atmosphere, so you should get a gut feel as to what you prefer.