The RX is a reliable one, but drives like an older, boring car (it's still a great car though). The MDX is sportier and bigger, but reliability is not great (I'm expecting it to get worse with the new ZF 9 speed). The MDX is getting a little old, especially in the cabin materials and infotainment, which is a deal breaker for me.
I'd much rather buy a Honda Pilot over the MDX because it is almost as nice as the MDX on the inside and has newer technology, but it isn't a luxury SUV.
If you want low depreciation and fantastic reliability, go for a Lexus. You might get more features in an NX because of the lower price.
The 2018 Audi Q5 looks like a great car, but depreciation might not be it's strong suit. Luxury cars depreciate the most, so maybe think of a top of the line Honda Pilot, Toyota Highlander, or Kia Sorento, which I was blown away with how much I liked it.