It totally depends on your location. On some of the location, Jio 4G can be better where as Airtel 4G can be better in some other places. But right now jio is free so I would say jio is better. Jio 4G is available on more Telecom circles than Airtel 4G so coverage wise Airtel 4G is behind Jio 4G but one the other side Airtel has less customer database of users so it maybe providing better speed at some locations.
As of now, Airtel 4G ihas a better better at some locations because of its strong network connectivity however jio may take lead in near future. You might try comparing both at your location since it also depends on location. Compare options are available at opensignal.com .
Jio is providing cheaper solutions but sometimes signals drop , non availablity of 4G network also speed is merely equal to 2G at some places making an unpleasent experience for user.
If you are getting equal signals and same data bandwidth, then use Reliance Jio because Reliance Jio is providing true 4G VoLte Network.
Airtel said that it will take 1 to 1.5 years for them to implement 4G VoLTE in all Tier-1 cities(not even Tier-2 cities). Looks like Airtel has a long way to go