Thank you for all the responses so far. It's making it harder not easier as so many clearly loved the schools they've seen their kids go to
One follow-up question: in terms of leavers destinations, my impression is that Broomwood and Thomas's have a big skew towards boarding and, separately, traditional schools, whilst some of the other schools mentioned seemed to send kids to perhaps less famous but more progressive (e.g. more co-ed schools). I'd love any thoughts and experiences of this from any of the schools mentioned.
My current expectation is that my son would stay at the prep school until age 11 and then move to a London day school.
For me, the key goal is to give my son the best opportunities but also those that are right for him. So, if he turns out to be academic, I'd love for him to go to a highly academic school, but likewise if he isn't, then I'd prefer an alternative path.
Another follow-up question: what is the advantage of the 'trust' schools over the 'businesses' schools?