bjt compared to mosfet
Well.. Its not always better..
JFETS are not used extensively as MOSFETs usually outperform them with the advantage of no gate current.
In Integrated Circuit:
1. In Digital, we use MOSFETs because they take a very small size and can make the required logic functions with a very few number of transistors compared to the BJTs. They also don't absorb base current as BJTs and also they dissipate less power.
2. In Analog, we have two cases:
i. We use MOSFETs as in digital usually because most circuits now are not purely analog, but mixed signal circuits including both digital and analog parts, so we use it because its already in the process, although we sometimes need the speed and gain and less noise of the BJT which is quite attractive.
ii. If you can get to a BiCMOS process then most of the HIGH SPEED analog parts are made using BJTs to make use of the advantages mentioned above together with MOSFETs for the digital parts.
In Discrete circuits:
BJTs are used extensively for their high gain and speed and less noise, as the working environment is usually noisy with high capacitance or load. Here the BJTs dominate and outperform the MOSFETs also becuase they are not ESD sensetive devices unlike MOSFETs. Also, in discrete circuits mostly the package sizes are large enough to make any decrease in the device size insignificant, although power requirements might still be a bottleneck for the BJTs.