In a friction drive motor, a small, solid wheel rotates against the side of the tire in order to drive it. The first motorcycles used the same concept, with a motor mounted above the front wheel. The problem is that the drive rubs at the side of the tire. It's inefficient, and it quickly wears the sidewall away. Tires need to be replaced every couple hundred miles. For this reason, you'll seldom see electric bikes with this type of drive anymore.
I tested the Sduro 8.0 towards the end of last year (there's a new range out for 2018) and was surprised by its nimbleness. You expect e-bikes to be less maneuverable than their acoustic predecessors, but, pelting down some bespoke forest paths near Pedal & Spoke in the Surrey hills, I found I completely forgot that there was a box of electronic EPO on my frame. Partly, that's because the battery is cleverly integrated into the frame to decrease drag; mostly, it's because the suspension is soft and the steering nimble, much like a normal mountain bike.
For many bikes, battery range is more important that total power (because they're all pretty powerful). You want a bike that delivers a range long enough for your rides at the power levels you want. Most e-bikes will have three to five levels of assist kicking in anywhere from 25 percent of you pedal power to 200 percent boost. Consider how fast the battery takes to recharge, especially if you'll be using your bike for long commutes.