While there are many reasons for selecting one type or make of EAPC over another, two considerations for an awful lot of potential buyers rank somewhere near the top of the list; one is price and another is weight.
Now, while not everyone is concerned by either, many people would like to be able to attach their bike to their car, two bikes in some cases. The Big Bear at 26Kgs is too heavy for most cycle carriers even minus the battery. The Oxygen MTB comes in at 21Kgs which, after battery removal, reduces the weight to under 20Kgs, the limit for high-end cycle carriers. Most roof or tailgate cycle carriers have a limit of 15Kgs for each bike attached so for the heavyweight models such as the BB, the only safe way for transportation by car is either inside the vehicle or on a towbar-mounted carrier.
In terms of price, the Oxygen at its current price seems great value for the power and quality on offer, (I haven't ridden one). That said, the Whoosh models have all provided fairly decent quality and power for quite a long time now. They appear very good value although again, I haven't ridden one.
I'm not sure I'd want to swap my Kalkhoff PC for the Oxygen though as it really is very good.
Tom