What is the difference in between BJT and FET current mirror circuit ?

 

The type of transistor that is used... What do I win?

 

Functionally it's more difficult to do accurate FET current mirrors because of the normal large manufacturing variation in their Vth voltages. The Vbe of a BJT is generally a much closer match between transistors.

 

Mosfet current mirrors are a strange lot and difficult to control (poor compliance).

 

In addition, bjt current mirrors work well enough on a monolithic chip, but discrete transistors generally need resistors in the emitter side to get them to match better, and getting them to track with temperature change is yet another consideration.