Millenia caps rewards on spends upto 1K i.e., you can spend till 1L in a billing month to earn rewards. But TNI doesn't and also the reward rate is 1.5%.
For edu and jewellery purchases TNI is the way to go for spends above 1L @1.5%. For spends below 1L Millenia is the way to go and can clock, quarterly milestone benefit of 1K AGV, effectively it becomes 2%.