I am using Airtel 4g for more then 6 months both wifi data card as well as their sim.
The signal strength and download speed is good but not good as they described. I hardly get 1.5mbps for download which is preety much less that what they show. Also there are connectivity issue with 4g.
If we go by the advertisement it come everywhere you go but in reality it is not even covering Delhi properly. In many places I get 3g sometimes 2g.
If I conclude then it is good if you are not a frequent travaller like me. Otherwise there 3g works much better.