AirTel is good for strong data network. But the huge problem is you won't get signals (even for voice call) in MOST of the places. Vodafone is good for data is its data charges starts counting by just turning on data network (with out actually using data) Idea is some what good. In my opinion BSNL will be the optimum choice. It has robust voice network every where and good data network at 3G coverage areas. Other operators are local based and their data and voice networks are very much unstable.