Firstly Drsomnath, this is an inspired thread, thankyou for providing such an excellent platform for discussion.
But then looking at these two anti-ship platforms, (from a neutral standpoint, ie, forgeting that one is Chinese and one is Russian/Indian), I would have to go for the DF21D, and not because its Chinese, but simply because of its capability. Let me explain:
In my opinion, the two differ very much in function, with each doing very well within its own sphere. The DF21D is designed to keep any CBG at arms length. Chinese policy is to employ area denial against a more advanced millitary, in todays reality: the US Navy. Denying the opposing power the use of his most flexible and powerful conventional units: CBG's, within China's immediate sphere of influence. A 2000+ km range DF21D does not allow any admiral in his right mind to move his most valuable targets into the kill zone. Even with in-flight refueling, air assets from the carrier would have a limited ability to operate in that area, contesting the air space with Chinese fighters who enjoy better support in terms of refueling and AWACS as well as possessing a definite numerical advantage.
Thus the DF21D basically removes US Navy CBG's from the equation, only leaving them with the SSN and SSGN option, who mind you, would then have to operate in SSK and SSN infested waters, whilst also being targeted by ASW air and surface assets.
The question then arises, can you do the same thing with a hypersonic CM with a 280km range? The answer is a definite NO. Sure it is much more flexible in terms of launch platforms, but lets analyse them.
Submarines: This is the ultimate in stealth targeting of surface assets. But then the cruise missile is not fire and forget, the target must be painted for them for until they are in range to identify the target themselves. This means, the sub must either paint the target itself with its surface search radar (which implies surfacing, and is thus extremely unadvisable), or relying on other assets to identify the target for them.
In this sense, the CM is the same as the DF21D in needing other assets to find and guide it to its target before it enters its terminal phase, implying that the use of either MPA's or helicopters. The notion that an MPA or an AEW helicopter can get close enough to identify an AIRCRAFT CARRIER, which operates within layers and layers of AAW protection is as I'm sure you realize, absurd. I'm not sure if the Indian navy can find and track surface vessels operating in international waters using space based assets, but this is how the Soviet navy planned to provide guidance when using sub and Kirov cruiser launched 400+km range Granit CM against US aircraft carriers in conjuction with long range bear MP aircraft.
The same applies for surface naval assets such as frigates or destroyers and air assets, ie. closing to within 290 km of a CBG, with carrrier-borne AWACS and destroyer and frigate pickets observing hundreds of kilometers around the carrier would be suicide in the face of precision munition and anti-ship cruise misslie equiped carrier-borne fighters.
Thus the hypersonic CM would be more useful if the opposing CBG was operating within its users EEZ, which is highly unlikely since CBG's operate far out to sea, well out the Brahmos's 290 km range.
That's why I conclude that the DF21D would be the more survivable option, (due mostly to its tremendous range).
Any thoughts?