Bosch sets the standard for eBike motors.  They are reliable, powerful, and have great response to rider input.  Being an entire system from motor to battery to display Bosch components work flawlessly with each other.  They have a 400ah and 500ah battery options and the ability to have two batteries on the bike to double the range.  They also offer several great displays, from simple to mini-computer.  BOSCH also has a shift detection that allows the motor to let off the power while you change gears to help protect the abuse a electric motor can do on a drivetrain.  Bosch motors also have a walk assist mode.

Brose has about the quietest eBike motor available.  The carbon belt drive allows for a quiet transition from coasting to power.  Some say it has the most natural feel in its power delivery.  Since they make only the motor there are lots of options for batteries and controllers.  Bulls has developed a 750ah battery for motor allowing for long rides and the confidence of going the distance.  They now offer several motors with up to 90nm of torque and 410% assist.   

The Shimano Steps motor is quickly becoming one of the most common motors seen on ebikes. There are several versions with the E8000 being the highest quality and is found on most eMTB's.  It is one of the lightest motors and has a great compact, color display that allows you to see your power level without having to read any print.  There are three power levels that are adjustable through and Shimano App at the user level.  My opinion after a few test rides was that it was not as powerful as its competitors and I felt the power dropped out before hitting the 20mph limit. 

The TransX M16 motor is found on many of the more affordable mid drive ebikes.  Although the specs say 65nm of torque the 350w motor has lots of power and assists all the way to 20mph.  I feel it is a bit heavier than its competitors and it had a few issues with the earlier versions.  We rent several bikes  that have this motor and they tend to be the fastest in our fleet.  Because it runs on 48 volts and is 350w it tends to eat through the battery a bit quicker limiting the range of the bike.