I've never done the Sunday brunch there but the last time GF & I were in HK almost two years ago, we really enjoyed the buffet at Hotel Icon's restaurant,
The Market. It was pricey, of course, but the quality of the food was good and they also had some unique offerings, such as a durian focused dessert section. I'm going to be back in HK in about a month and I am planning to partake in the dinner buffet at The Market again.