Google, Audi, Nissan, Daimler, Ford, Tesla, Amazon. They are all in one way or another working on autonomous vehicles and all working very hard to get their solutions out there the first. Some claim they will do so as early as 2015, others have announced their plans for 2020 to see the light (and hit the road).
True, Amazon announced their autonomous delivery drones today and they will be airborne over cars on the road. But that would in theory make managing such a large fleet perhaps a bit more complicated, while on the other hand it would be easier as much of the drone design is already done. Another bonus is that while carrying packages, they can probably get permission earlier compared to when they would carry passengers instead.
Really looking forward to see this play out, it will become most interesting to see (and participate in) this. The autonomous race is on, may the best robot win!