Electric Bike (eBike): Freewheel or Regenerative braking? Not asking for opinion which one is better, so please do not state without some reasons why one is better than another on eBike.

Question is: Freewheel or Regenerative braking is more efficient in Electric Bicycle?

So far I got:

Freewheel:


When battery go flat you can use it as a normal bicycle, while with
RB it feels like riding with a flat wheel (or even worse). 
It is lighter than hub with RB, and cheaper
Similar to a bike


Regenerative Braking (RB)


You can charge your battery up whenever you need to stop, albeit minimal. 
It helps you brake the bikes gradually, especially on downhill section, just like how motorised vehicles work.
Akin to motorised vehicle
Freewheeling is almost always better. 

If a freewheel ebike control system fails, it reverts to being a regular bicycle and you can pedal home. Otherwise, you might find that you cannot even push it home if the motor is stuck on heavy regen.

Furthermore, there is very little energy that you can regenerate from a bicycle. There just isn't enough mass or significant enough velocity to make it worthwhile. The regen also makes braking more complicated than it has to be as you need to swap out your brakes/brifters with ones that have brake-switches in them. 

On a vigorous discussion on the EndlessSphere forum, Justin Le pulled out data from his cross-country trip. While he did get 18% regen going down mountains passes, he also only got 1-2% regen touring over rolling terrain. His urban regen data was 11% which is close to the 10% figure that is used as the rough estimate of range extension possible.


  So, although this is a just from a single run, you could easily conclude that we'd expect about 5% regen for city riding in mostly flat terrain, 10% regen for city riding with lots of moderate hills, and probably more like 12-14% regen if there are really steep hills. 


Since e-bikers tend to recharge every day and each recharge is only 1-2 cents of electricity, increasing range and efficiency  a modest 10% just isn't  as important as it would be with a hybrid or electric car.