I use airtel for internet on my mobile but not because it's fast but because it has more network around the area.
I have problems with the 4g which doesn't work so I have to use 3g and whenever I called costmer service they say We are updating the network around your area to 4g which doesn't make sense because it's hasn't been good for past couple of years.
The charges are also a little higher compared to others for long prepaid plans but you don't have much choice.
It is true that it has good speed on some areas but where I live it's only decent.