What are the differences between fiber optic connectors ST, SC, MTRJ and LC?

Functionally, there is no difference. The primary reason for choosing one connector over another involves the evolution of the market for connector preferences, interoperability with like interfaces, optical loss insertion and port density. Newer interfaces such as MTRJ and LC have a smaller form factor, higher port density and lower optical loss than predecessors such as ST and SC. Each connector type is capable of carrying the lightwave frequency (measured in nanometers), shared by the other connectors.