StaadPro is the most widely used bread-and-butter structural software in Asia and the UK while SAP2000 seems to be the most widely used one in Latin America, Portugal, Italy and Spain.
The grids provided in SAP makes it easier to create the geometric input than with the StaadPro. Dynamic analysis is stronger in SAP2000 (earthquake force applied in any direction, automatic lumping of masses for earthquake, live load reduction, bridges transient loads, eigenmodes and ritz modes, etc...). Sap2000 has facilities for creep and shrinkage of concrete. SAP2000 program has the ability to solve heterogeneous soil-structure interaction which is not possible in StaadPro. Also, SAP2000 can import the geometry and the material properties of StaadPro models, I am afraid that the opposite is not possible.
However, StaadPro has some great advantages. First and foremost, the license is cheaper. The connection with visualization and drawing software is much easier, not in vane StaadPro is a product of Bentley (Microstation, PDS, etc...). StaadPro provides additional modules for designing steel joints and foundations. The text editor facility for the model input file makes StaadPro is more versatile for model modification. It is possible to work with the ASCII file of SAP but it is cumbersome and it is necessary to leave the model and reload.
Now, the choice is yours.