honestly, get your kids admitted in islamabad convent school
i myself am a graduate from the city school, it is good if for your son, but never ever get your daughter admitted in it.
as far as drugs and violence is concerned, it depends upon the kid and your brought up, i have seen alcoholic drinks and weed in school a lot of time but by the grace of god i havent even touched any of them... so you cannot really blame the school.
basic education is important for your kid, because this will effect how he grows up to be.. all schools are almost equivalent, city school and becon house are good in this regard as their basic education is quite western based and they groom up the children good, give them self confidence and they are almost always having different extra curricular functions every week to hone the kids skills..
one piece of advice never go for all boys or all girls school, 90% of the kids turn out to be gender shy for the rest of their lives or desperate.. (please read it again 90%.. and not 100% haters stop writing against me :P)
never get you daughter admitted in an imcg,girls over there are quite famous all over pindi islamabad.
froebels roots headstart and west minster are a no no.. very very bad discipline there..
my younger sister is in convent school and i personally like the discipline and security there is for a girl. there is almost no violence. although they mix a little of Christianity in the school.. but i think thats for the good, we must accept other religions and try to be friendly with others instead of hating them. islamic teachings are mostly taught at home best.