If you travel by flight once in a quarter, then MMT Platinum is better as you will get 1 lounge access per quarter (need to spend 5000 in previous quarter though)
Both can be used when any e-comm enables offer...
MMT Platinum has negligible fees as you pay 500+GST but get Rs. 500 MMT Voucher which can be used for hotel/flight booking so you only pay GST with no annual charges
The only thing is that in case of MMT cards, the points will be accumulated in MMT wallet instead of payback points... so you can use MMT wallet for further air/hotel bookings too