King of the hill - Bosch Performance Line CX drive engine is the strongest of all of the current big three motors - whereas almost every other drive has a nominal (aka continuous) wattage rating of 250, the CX is rated at 350 watts and 75 Nm of torque. Although nominal motor wattage is primarily to comply with EU regulations (and off road there are less restrictions).
Bosch's most powerful motor is tuned for climbing off road fast, and it is the fastest climber in real world testing, and is also popular for sporty street riding in hilly areas. The Performance Line CX drive unit is Bosch's flagship motor, has what Bosch calls Uphill Flow - support already starts at very low pedal frequencies – this makes it easier to set off uphill or to drive out of tight curves. Turbo Mode, the engine support goes up to 300% - even at high speeds. It is also a great motor choice for heavy cargo bikes facing steep hills, or really for anyone who wants no compromise climbing and a bike limited to 20mph assistance. A street setup popular on Riese & Muller is to run the CX motor with either Rolhoff or Nuvinci internal gears using a clean & quiet Carbon Belt drive.
Shifting under load on an eBike can be a challenge, especially going up steep climbs where even a second off the power and it is back down to the bottom to start again. On human power alone, a rider intuitively backs off the pedal torque ever so slightly for micro-seconds, and that allows for a smooth shift. On eBikes the motor doesn't know you want to shift and what can happen is that even if you have switched gears, the derailleur in back is not able to move the chain up to the next sprocket because it is under tension from the motor. Being the wrong gear can mean losing precious human and motor power on a steep ascent, so timing your shifts just right is critical for a good off road experience.
All of the motor systems address this in their own way, but Bosch's shift sensing technology gives them an important edge on climbs because they measure whether the shift cable actually moves. Brose and Shimano "infer" that a shift change is coming by sensing the amount of torque a rider is putting out to lessen assistance for that micro-second to allow a shift, just like it works on an unassisted bike. Both work - but riders seem to be split on preferences for each style. You should test ride both and decide which you like better.