I liked the AU Swipe up platform which is specifically designed to apply on C2C (from what I know, most of the banks deal with C2C through their agents offline). With swipe up, you put details of your best card and it suggests you one from AU with enhanced limit and also shows a comparison of your old vs their card. In my case I put in information of my HDFC Regalia with 3.3L limit and got ACE Ultra LTF with 4.95L. Honestly I did not need a card but was impressed by their generosity so went ahead. I sometimes use it online to get around 2% cashback (all online transactions) and 1+1 movie offers.
Nothing very fancy about their swipe up cards but does not hurt since they offer LTF.
One more reason I applied for the card was that I can later apply for another premium card on C2C basis using this due to it has higher limit (Higher chances of getting cards like Magnus).