They're both seemingly doing well, but only one is plugged into an unwavering trend that's built to last.Uber Technologies (UBER 1.10%) and Carvana (CVNA -0.44%) aren't just two different companies. They're seemingly polar opposites. Ride-hailing giant Uber is thriving largely because owning and driving a car is an increasingly expensive hassle. Used car dealer Carvana, conversely, makes it easy and affordable to own your own automobile.One could reasonably argue there's solid -- even growing -- demand for ...