Because e-bikes are capable of greater speeds for longer periods of time than standard bikes, you want extra control. Wider tires provide traction and some bump absorption with little penalty. You also want strong brakes to slow you (and all that extra weight) easily. It's worth looking at the quality of the brakes and investing in bikes with better ones if you can.
Twice the speed - with half the effort, Optibike has the power. On a test ride in Boulder Colorado, a fit road cyclist was able to climb the notorious Old Stage Road at 10 MPH sitting down with an easy spin on the Optibike. On his ultra light road bike, he had to stand and grind all the way to go 5 mph!!! Twice the speed - half the effort, Optibike has the power.
E-bikes mostly use motors and battery options from a few major suppliers: Bosch, Yamaha, Shimano, and Brose. A few other brands exist, but are less reliable or powerful. Some, like the Yamaha system, have more torque and others are quieter. But generally all four make good options. Look for motor output (in watts) which will give you an idea of total power. But watt hours (Wh) is perhaps a better figure to use—it takes into account battery output and life to give a truer reflection of power.