Hi @Confusedmom53 ! May I offer a slightly alternative analysis? I work in the education sector and we look at schools, including leading independent schools.
Clearly, all the schools you mention are very well known. Yet each has a distinctive current and historical character, something beyond statistics. All are good schools and all cater for the most academic boys. Your son will be fine at any of them. My family knows boys at all of them and they all like their school. Generally, travel considerations and family or community links prove decisive for many families when they decide between them.
Firstly, does UCS now admit girls into its Sixth Form? Something to consider.
Habs has generally been the most academic and is still widely considered to be so. City is the most distinctive because of its location; the commuting is reckoned to help with boys’ maturity, self-confidence and independence and exposure to the City itself and nearby, major, arts venues can be inspirational. I would choose between these two, especially as convenient, on-site sport is not such a big deal for you. You mention particular, current interests and these will be nurtured at each. But don’t be surprised if, aged 16 or 18, your son’s academic or extra-curricular focus and passion lie elsewhere. The best school will bring out something you and he may not even know is there at this stage. (This happened with our child at her school, both academically and musically.)
‘Too many South Asians’? For some years, the worldwide trend has been that Chinese, East Asians and South Asians target selective schools and are disproportionally represented in them. They only target the ‘best’ schools. (I know one Iranian lady who sent her daughter to one school partly because it had a lot of South Asians and she regards South Asian achievement highly!) We know that outer NW London has a significant South Asian community which cherishes academics and cricket and so Habs works for them, as does MTS to a great extent. Diversity? Most of these pupils are regular, fairly cosmopolitan, British kids who are comfortable with peers from all backgrounds. Ultimately, your friend is your friend and that’s what counts. Students are often better at multi-ethnic and multi-cultural friendships than their parents are. And university will only develop this further after high school, so it's not just about the 11 plus school. (My daughter’s school had a lot of Asians. Yet today her closest friends include Irish, Swedish, Jewish, and Euro-Afro-Caribbean individuals.) Perhaps the most powerful modern education is learning how to work in a team, how to behave in a group, how to get along with people and how to make friends with people who look different from us.
Which would I choose? I would be tempted by City. Congratulations to you and your son on gaining such offers and earning such a choice.