a good rule of thumb pulled from this forum thread (http://www.electro-tech-online.com/general-electronics-chat/39339-mosfet-vs-bjt.html): Need a switch to be fully-on fully-off and carry lots of current -MOSFET Need a switch that needs to have lowish capacitance – BIPOLAR Need a cheap, dirty 2 or 3 component current source – BIPOLAR Need a low voltage/noise amplifier – BIPOLAR Need…