What factors play into choosing type of MCB (Circuit Breaker) which is B16 vs C16 vs D16?
Your specifications on type B, C and D MCBs are incomplete. The crucial detail is that these are the overload currents they will tolerate for a maximum of 5 seconds. All of them should trip if they experience a current above their rating for longer.

The MCB type you would choose for a circuit therefore depends on the peak transient current you expect your load to draw. For most applications type B is perfectly adequate, but for circuits that supply very reactive loads such as air conditioners, motors and other machinery, large switch-on currents would force you to use C or D. The manufacturers of such devices will normally specify details such as supply cable size, MCB capacity and type and local wiring regulations may also restrict some of these choices.