I know MOSFETs are much more efficient than BJTs in that they don't consume as much power when on whereas a BJT consumes base current the whole time it is on. I also know that MOSFETs tend to fail shorted. I can't find any information on BJT failure modes though/do they usually fail open or closed. Does anyone know about this?
To address the first part of your question: It isn't true that MOSFETs are always more efficient than BJTs.
In high-current applications, the I2R losses in a MOSFET can far exceed the ICVCE(SAT) losses in a BJT. This is why IGBTs are often preferred in high-power equipment.