[prestonee]

A key note: Op amps are made from transistors.

BJT transistors are the most commonly used due to lower inherent noise levels than a MOSFET

MOSFET transistors are also used in opamps, primarily custom chips using digital and analog since CMOS process is cheaper than a bicmos process. Also a mosfet has lower gate leakge current then a BJT so low power Op amps use Mosfets

JFET transitors are fairly rare in Op amps but do show up in very low noise Op amps at least in the input stage due to their very low noise characteristics.