In purely terms of backbone infrastructure i.e., domestic and international which would be in terms of bandwidth capacity and not the hardware capacity itself then Airtel is the better one here.
Jio is still at a building level, but it is nowhere close as the vast infra of Airtel. Even in many out-sea's countries, Airtel owns its fibers instead of leasing on an L2 capacity.
Down point of Airtel is their hardware which is a serious aging issue and lax SLA assurances, while Jio is very up to the task and went balls deep in first go it still majorly relies on transits and limited interconnect IXs to get their packet through.
They both have their pros and cons; nobody is perfect.
Eg. Jio's interconnectivity to peering.cz is abso garbage. Airtel heavy over-reliance on Hurricane Elec (which used to be a good transit, now not so much) has demolished performance.