Platinum is always, ltf and afaik there are no major benefits other than dineout benefits if you use eazydiner for payment. Signature card is good as you get 2 free movie tickets every month but it is difficult to get it as ltf.
I have imperia banking relationship with hdfc but its not that great. I don't see any benefit except for getting free locker facility which I'm still unable to get it. Rm only calls for selling ulips or similar products.