FET has high input resistance (approx. in order of 100-M ohms for a JFET and 1010 to 1015 ohms for the MOSFET). Thus, the FET is a voltage-controlled device, like a tube, and not current-controlled, like a conventional transistor.
It shows a high degree of isolation between input and output.
All field-effect transistors are unipolar rather than bipolar devices. That is, the main current through them is comprised either of electrons through an N-type semiconductor or holes through a P-type semiconductor while conventional transistor is a bipolar device relying upon two types of charge carrier, electrons and holes.
The FET is less noisy than a bipolar transistor.