Among all companies, Amazon feels like it has the most defensible moat to me. It's fulfillment network represents hundreds of billions of Capex, and will be capable of delivering many millions of products same day before too long (it's already doing <12 hour delivery where I live pretty regularly). 

So many profit levers still left to pull, advertising TAM will keep expanding as delivery times shrink (there are tons of items that you "need now" when you need them - if you can get those items on Amazon then those companies will spend more on adds there - for example Charmin TP - I think Amazon still has lots of CPG ad share to steal). 

Amazon seems more likely than anyone else to do something really special with healthcare. 

And, once driverless cars are a thing - won't that just be an add-on for Prime? The driverless car business is going to be extremely capex intensive, require intense optimizations, and will likely not be very profitable as a standalone. Sounds like it's right down Amazon's alley b/c they are quite adept at figuring out how to profit from things indirectly (e.g. they make money on adds and third-party services on their marketplace - which itself could run at breakeven indefinitely due to these other profit centers).

Plus it has AWS as we head into the age of intelligent machines?