My vote goes to St. Christophers as well; was always excellent. No-one has mentioned the American School. Is it still going? Was always highly thought of but very expensive.
One thing re. St. Christophers; maybe it's changed. In my time there were two schools; the junior in Budaiya & the senior at Isa Town. If your kids are spread over a bit it gets a bit hectic running around the two schools. This is years ago, maybe it's changed.