They are equally vulnerable.
Quantum attacks on the hashing algorithm are utterly irrelevant. The best quantum algorithms give you a big advantage in making hashes, but doesn't let you make them at will; the difficulty will adjust and life will go on. The only relevant quantum attacks are on the digital signature scheme that protects wallets from thieves, and both Bitcoin and Litecoin use ECDSA (which can be broken by Shor's Algorithm).
OK question answered, blockchain safe, wallets fly open...(except for the send once to new address always scheme)
