Data works everywhere with BSNL, it even worked at places like Chumathang and Durbuk. Speed is usually slightly faster than what you will get at Leh , but still 2g.
No 3g connectivity as of now.
Vodafone postpaid works in Leh and a handful of places, but it is a fairly choppy network (it doesn’t do roaming on Airtel, some other network). Data is also not free; you have to pay 12 paisa per 10kb.
No idea about Reliance.