Luanda only looks like that in a very few select areas. I have it on pretty good authority (friends who have worked there) that the skyline is quite deceiving - it's not a great place to be. It being the "most expensive" city in the world was largely due to the fact that expats had very few options as to where it was safe to live / go out.
Kigali is apparently a very clean city and is known for a burgeoning arts scene. The former is do to some heavy handed policies on littering but I guess the end result worked.
Since we're posting pics here's some of Johannesburg by a photographer there who's work I enjoy: