ISB has gone down the drain since last year. They made an idiotic move of accepting 720 candidates leading to a free fall in the rankings.
IIMs rely too much on theory than real life stuff. And you can't really create much of a network here, because of the Indian mentality of undermining everyone.
I feel by going abroad you get a chance of creating a vastly superior network with people from numerous nationalities and background, something that Indian schools have yet to even do.
Moreover their course structure and teaching method is quite different and inline with current ongoing in the world.