MHS has an extensive sport and co/extra-curricular program, just saying. Clubs for just about everything, pretty heavy student leadership opportunities, heaps of affiliation with organizations outside of the school etc.
If I had a younger sibling in this scenario I would personally prefer him/her to go to JMSS. The selective atmosphere where everyone is smart really does pull you up academically, and opposed to MHS/MacRob it is actually a co-ed school which I think eliminates a few of the negatives of those schools. The amount of (excuse me for the phrasing) socially inept boys and girls that come out of the school is somewhat concerning, it is definitely a minority, but still a big concern in my opinion.
Haileybury girls school does offer scholarships more regularly compared to the boys school from what I hear (someone with better knowledge please confirm/deny), and I do find that from my peer group outside of school, a lot of kids have been dragged down into some pretty bad stuff as a result of going to private schools. Whilst it's not something that is non-existent at selective schools, I tend to think there is some correlation between an academically elite cohort, and a cohort which is generally the "right crowd" you'd want a friend/sibling to be in.
That said obviously private schools (or any other school for that matter) do produce good students, and in the end most of what you get out from your education is based on your own attitude.
/My 2 rupees