They're both overpriced trash that GM and Ford sells people who are solely label whores.
An Escalade is just a Chevy Tahoe and a Navigator is just a Ford Expedition. They literally just throw a different logo on the front, a better stereo system, and maybe some better leather in the interior and charge $30,000-$40,000 more lol
If I had to pick though I would probably go Escalade, just because I like a lot of GM shit better than Ford shit.