August in Hong Kong...you should be able to do better than that, I'd think. Have you tried AsiaRooms.com? The best views are from Tsim Sha Tsui, and both of your hotels are on the Island.
If they were the same price I'd go with the Conrad, but they're not, so I'd go with Grand Hyatt. Your post is a little unclear as to whether the discount is already reflected in the price, however.
I still think there's a better deal out there for you.