I find that very odd; I haven't noticed that much of a difference between any of the taxi-like apps I've used. I almost always end up sitting in the front, especially in Austin.
Plus, don't most drivers drive for both companies at the same time?
That's a surprising experience, I take an Uber at least 2-3 times a week in the bay area and I sit up front almost every single time, unless I have a package with me. I have never been asked to sit in the backseat, even after >700 Uber rides.
Here in Portland almost every driver uses both apps so I don't find a difference in driving. I prefer Uber simply because there's less expectation of tipping and the price is about the same.
I always sit up front and talk with the person, learn what else they do, how long they've lived in the area.
When I try this with Uber (esp in SF), they often show me a thumb pointing towards the backseat instead!