I have a DD in the 6th form at C&S.
She has been very happy there (joined in YR7) and achieved very well academically. We have always found the staff positive and caring. The majority of the students seem well behaved. I am sure there are exceptions to this, but no more than you'd find at a comparable school.
There are lots of sporting opportunities, plus dance,drama etc. etc. Students are able to take the Dof E awards . There are plenty of overseas trips on offer.
When we visited the grammars in Bexley, this is the one my DD , my partner and myself got the best feeling about and we felt was most impressive in terms of the students taking the tours and the Headteacher's speech(liked that they emphasised that effort would be celebrated as well as success). Having said that, I would have been happy for her to attend Bexley Grammar or Townley, but C & S was our first choice.
I don't think you would be disappointed in either school, you will just get a better 'feel' for one over the other. Good Luck