One of DC finished BGS 6th Form having previously been at CHS (they moved as wanted to do a particular A Level which CHS didn't offer at the time). They are very academic and now attending Durham Uni. Had a very bright cohort in their year at CHS, and also loved their time at BGS. We were very impressed with the attainment at BGS - fantastically supportive teachers, great opportunities available, lovely camaraderie amongst students at house events.
My other DC is still at CHS (has some SEN), and it's been a great place for them - currently on track for grades we never thought were within reach, again their teachers have been so kind and supportive of their needs. Lovely pastoral care.
We don't live in town, so never considered city comps, we live near a fairly well regarded comp, and who knows, it may have had the same outcome, but for our DC with SEN, I think they would have been eaten alive TBH, so we're happy with our decisions.
Good luck, it's a very trying time making the decision- you don't get to try again, do you? A friend said to me that whatever decision we made, it wouldn't have been wrong, and I took quite a lot of comfort from that.