Depending on what you want to do will dictate where to stay.
HK is comprised of three areas: the peninsula portion Kowloon, the area adjacent to that called New Territories, and then the HK Island itself. All of these are accessible by MTR (train, mostly underground).
I personally stay near Jordan station in Yau Tsim Mong district of Kowloon because:
-It's very walkable to everything I need (can walk to the Harbour, main shopping area, Ladies' Night Market, LangHam Center)
-Express bus to and from the airport is right on Jordan Road
-Fairly central to a few of the MTR lines
I know nothing of Macau as I haven't been. Highly recommend Cheung Chau Island though. Day trip or overnight. It's a small Island, touristy for hiking etc. The whole Island has no vehicles except commercial. Most people bike but the whole thing is very walkable.
My favourite hidden gem for food:
http://www.etfoodvoyage.com/2016/02/...em-in-stanley/