Want to bump this thread as I too was in same Dilemma. This is quite confusing for everyone who hold Millennia CC and want to get hands on a more premium CC. Both cards are good, but it majorly depends on your expense.
If your expenditure on CC is moderate (around 50-60k) every month including travel (flight/train) and hotel bookings, then it makes sense in getting Regalia for fetching those bonus RPs and then using the same for booking next time.
But if your expenditure is around 20k-30k for say 8-9 months and touches 60-70k only once or twice in a year, then it makes sense to have Millennia instead. This is because the 5% category is capped at max 1000 Cashback Points per month, which means you can spend 20k every month on Amazon, BookMyShow, Cult.fit, Flipkart, Myntra, Sony LIV, Swiggy, Tata CLiQ, Uber and Zomato and get those points. Another plus point being 1RP=Rs.1 in case of Millennia.
So, If your monthly CC usage is at lower end and you tend to use these 10 apps (mostly), then go/stay with Millennia, but if you are a moderate user, then go with Regalia.
For people spending 1 Lakh or above every month, go with Super Premium CCs like Magnus which will give Bonus RPs for monthly reaching milestone
