It would be Spoken Hindustani(Hindi+Urdu). That I will make approx 45% first language speakers and around 55–60% 2nd/3rd language speakers.
Even in first language Hindi speaking states like Rajasthan, Bihar, Chattisgiri, Himachal, Haryana many people will talk in their local languages/dialects within themselves but Hindi is taught in schools and is widely used.
In Written Official Usage nationally English easily beats Hindi and all technical education is in English.
