3 nights in Macau is too long so for that alone I'd do GH HK. There's so much more to do in HK.
In your definition, GH HK is iconic - since it's a convention hotel in HK soooo many of us have stayed there many times. If you don't stay, you'll feel like you missed it on your list.
I have keynoted many conferences there so always have good memories of GH HK, even though I don't particularly love the size of the rooms or the service.
But almost anyone who is loyal to Hyatt has stayed there - I even stayed there many times when I was loyal to a Starwood because of the conventions