How many miles do you think you'll be riding in a day?
Hills?
Will you want to travel with your bike (Car rack)?
What do you think you want your maximum assisted speed to be?
I would start with the frame type you want. Some bikes have aggressive riding positions, which can optimize aerodynamics or pedaling performance. People with bad backs or necks may find those intolerable - others may just find them uncomfortable. Can you swing your leg over the high saddle easily, or will you be carrying things on your rear rack that make the leg swing clearance height too high? If so, consider a low-step frame. If the roads are good where you ride, you may not even want a front fork - or if you do consider bikes with them you may want one that locks and/or is adjustable.
For on-road use, I personally advise against fat tires. I know some people like them because they adsorb small bumps and make the ride cushy, but for me the penalties are heavy steering and increased unsprung mass. Again, if the roads are good then you should looks for bikes with narrower tires, under 2". There was a recent push towards "Plus" tire sizing, which were tires approaching 3" in width. Not as wide as fat tires, but wider than typical mountain bike tires. For on road you don't need these, but you may like the additional cushioning, if heavier steering. This is an area in which you should do some test rides to see what you like.
The same is true for cadence sensing versus torque sensing. Cadence sensing is like a throttle on your pedals. As long as the cranks are moving, the bike will give assistance depending on the power level you choose. That can be fun, as at a high power level you can go really fast with just an easy cadence, but it's not the best workout, and there will be times when the power boost is not what you want or even dangerous in traffic. WIth a cadence sensing bike, you will be constantly changing the power level based on hills and such. Torque sensors are almost always better - they make the motor assist based on how hard you're pushing on the pedals. Push harder and get more assist. The power levels control the multiplier, so you're not changing them as frequently. Not all torque sensing motors are the same - the differences are in control and feel. On a good torque sensing bike you're actually not aware that the bike is helping you - you just feel like superman up the hills. That's a combination of available power/torque and software programming.
The RadPower and Juiced bikes both use hub motors. There are also mid-drive motors, which power the cranks. Within the hub motor category there are two types: geared and direct. RadPower has a decent blog entry on the pros and cons here:
https://www.radpowerbikes.com/blogs/the-scenic-route/guide-to-electric-bike-motors . Hub motors are good for on road use. If you have hills then you'll want a geared motor, but if not then a drive drive motor might be preferable. Mid drive motors have advantages of less unsprung mass, but they power through the chain, so you have to be in an appropriate gear like on a normal bicycle.
Another aspect is brakes. Generally, hydraulic brakes are better than mechanical brakes - more stopping power with less lever pressure required. This matters is you're a big person traveling very quickly, and/or doing steep descents.
Finally, you said class 2 or 3. Depending on where you'll be riding, Class 3 bikes may be prohibited. That may not matter to you, as enforcement in the US in many places is non-existent and even difficult, as many Class 2 bikes can be programmed to run at Class 3 speeds.