MOSFET and BJT transistors
This question is really broad.


MOSFETs switch faster as switches (they transition between zero and full conduction faster). BJTs are faster (have higher bandwidth) as amplifiers devices (BJTs can move around within the "partially on" region where linear amplification occurs faster.
BJTs need continuous signal current to control. MOSFETs do not (only voltage and transient currents to charge the
gate-source capacitor). This is a strike against BJTs in high power circuits where your control current is proportional to your load current, or in amplifiers where the source impedance is very high and can provide very little drive current.
MOSFETs behave as a resistance when fully conducting. BJTs behave as a diode. This is a benefit for lower voltage MOSFETs (&lt;200~500V) since the voltage drop for resistance is less than the voltage drop for the BJT which means it runs cooler. But as you construct the transistors to tolerate higher voltages, the MOSFET resistance increases to a point where the voltage drop is larger than that of BJTs and the BJT becomes more efficient.
MOSFET minimun gate voltage to get it to conduct is higher than the minimum base-emitter voltage required to drive a base current into a BJT to get it to conduct (at least for now) . Important if you are using very low voltages to control a transistor switch.
MOSFETs have a parasitic anti-parallel body diode (i.e. they can only block
current in one direction). BJTs do not. This can be good and bad. In some circuits with inductive loads, it means you might be able to get away without an external flyback diode and instead rely on the body diode MOSFET, even though you really should have an external one optimized for the task.
MOSFETs can current share (put in parallel to share a load current) more easily than BJTs without thermal runaway.
BJTs have higher transconductance so tend to work better as amplifiers.
BJTs are lower noise. Better for sensitive amplifiers.
For integrated circuits, BJTs are easier to match (provides numerous advantages for analog circuits), but MOSFETs can
be fabricated are smaller (required for high density digital circuits).