I have been using airtel from last few years and it has best network coverage. Althought bit expensive than others but much better services. You always get what you pay for. Their 3g speed is best among others but still they need to work on that. Sometimes I only get 2g signals even when iam paying for 3g.Their customer service is also good. Their is some issue with their website as it takes really long to upload.
If you have no issues with high charges and want best service than I can personally recommend airtel network