In my area where when mobile phones became a necessity not most of mobile operators were working I tried every one of them.
But to avail then someone suggested me to take a airtel sim which I did only to my amusement that it worked pretty good almost anywhere in my house till now I have been using Airtel regularly.
Airtel has come a long way since then although the rates of calls and data have jumped up but one thing remains the same and that is reliability as I can bank on a Airtel sim to keep me connected in most remote places, there were also times when I could not afford Airtel data plans(BEING A STUDENT) but to makes it remained there always. If ONLY Airtel would drop its call and data charges I could safely say it is THE BEST atleast in my area.