Because I'm originally from Bombay too, I'm less concerned about pollution as Shri says. For the same reason, I'm less concerned about most other things too. I went to a pretty average school on the middle-class scale in India and so did my husband. However, we have no problems competing internationally. So I'm not that bothered about my kid being in the "best" school. In fact, I'd probably prefer he wasn't. I find the whole snobbery associated with these schools and the desperation of parents to get their kids in weird.
If I had had the energy, my first choice for my kid would be a local school like Roger's kids. I would love my kid to speak Cantonese and have Chinese friends instead of living in an English-speaking expat ghetto. However, having done some research, I feel I don't have the energy to do what it takes to have a kid in a school where the medium of instruction is one I don't understand. So an English-medium school it will have to be, though I might try a Canto kindergarten and see if my son likes it.
My concerns would be:
1. Are the teachers nice to the kids (maybe this is my Indian background where teachers were routinely mean if not physically abusive)
2. Is there bullying in the school? How would an Indian kid fit in? Would he face racism from either the teachers/students?
3. The economic profile of kids in the school. This is my problem with even ESF - because of the fees are quite steep, the economic background of the kids would have to be affluent, relative to the average in Hong Kong (i.e. the local average, not just expats). I would rather my child mixed with kids from a diversity of ecomic backgrounds so that he doesn't land up with a view of the world in which everyone lives in Mid Levels and has a car.
4 (maybe) how much homework and rote learning do the kids have to do? (again, as an indian, I'm used to a lot of homework and rote learning, and most people I know survived the sytem and thrived after but I am aware that it could also cause a serious aversion to learning).