Out of the following contenders:
1) GM (+Cruise Automation), Mercedes or VW with their enormous supply networks, vendor lock-ins, economies of scale and ability to massively ramp up a car production when needed.
2) Tesla with their (allegedly unique) battery storage tech, working manufacturing facility and massive amounts of data harvested from thousands of Tesla vehicles on the roads today.
3) Google/Waymo with their unlimited budget, ability to partner up or buy whoever they choose, and nearly limitless amount of software engineering talent they can suddenly relocate to this project when desired.
4) Avis/Budget, Hertz or other fleet management company that already has a relationship with car manufacturer and can own/maintain/wash/clean/park/dispatch a large number of vehicles on the cheap.
5) Uber.
Why is #5 the strongest candidate? Does the dispatch app that displays available cars on the map create such a strong moat that #1, #2, #3 or #4 will never be able to replicate? Does Uber have a bunch of aces up their sleeve that will allow them to build/buy automobile manufacturing facilities on the cheap? Do they have a know-how of maintaining a large fleet and take care of simple things like changing a tire or cleaning the car after the previous passenger puked in it? And do that at scale?