Believe me Chhatrapati Shivaji Terminus (CST), formerly Victoria Terminus (VT), is the most attractive and historical buildings in Mumbai.
It was designed by Frederick William Stevens who was inspired and influenced from Victorian Italianate Gothic Revival architecture and traditional Mughal buildings.
The huge station was built in 1887 in the Bori Bunder area of Mumbai to facilitate the Golden Jubilee function of Queen Victoria.
The new railway station was built on the location of the Bori Bunder Station and is one of the busiest railway stations in India. It serves as dual terminal for both long-distance trains and commuter trains of the Mumbai Suburban Railway.
In March 1996 the previous name was changed to its present one and it is now known simply as CST (or CSTM).
As I always say that South Mumbai is actual Mumbai where you get the feel of old culture and victorian era. Rest of the city and Navi Mumbai is just like any other crowded cosmopolitan city, a concrete jungle. So my vote goes to south Mumbai.