Right now I am using Galaxy C9 PRO and my wife is using A9 PRO. Both are very good. Jio has CA using Band 3 + Band 5 (1800MHz and 850MHz) in most places and in some recent sites its Band 3 + Band 40 (1800MHz & 2300MHz). A9 PRO supports them and I have experienced great speeds. Though Samsung doesn't show LTE-A or LTE+ in signal, we can confirm them via dialing *#0011# on native dialer.
Right now I am using C9 pro, because it is having SRVCC facility, which is NOT available in A9 PRO. My main number is in Airtel. Airtel has started testing VoLTE. SRVCC allows calls to fall from VoLTE to 3G without DROPPING it, when we are on call while moving from 4G coverage to 3G or 2G coverage. Only SD625, 626, 630, 653 (used in C9 pro), 835 currently supports SRVCC (not sure about lower end ones). Even SD821 (used in OP3T and LG G6) or 652 (used in A9 PRO) doesn't support SRVCC.
But A9 pro supports many LTE bands, including upcoming 700MHz one on Band 28 and 900MHz on Band 8, both are not supported in C9 PRO (at least not till now, may be enabled later via update). Further A9 PRO has better battery life (5000mAh vs 4000mAh of C9 pro) and very very cheaper now.
Advantage of both phones is, you can use Airtel for DATA on 3G and still get incoming calls on JIO. It is great feature to use, where Jio data speed is too low, but you want to get calls on both numbers. This feature is supported in very few phones, mostly Samsung. Go for any of them, you will be happy, imho.