Airtel 4G LTE is horrible at-least in Kolkata. I would give them 2/10 only because their billing system seems to be excellent. There is nothing good about the service though. Browsing is a nightmare! Downloading a 1GB movie means constant checking (if you are downloading without a download manager then God save you).
Conflicting IPs, constant disconnection, very slow speed are just some of the things which will frustrate you to no end. I never get all the 5 towers in the network connection at my place.
Overall go for Airtel 4G LTE only if you have a perfect life and are looking for something to screw your happiness.