I enjoyed reading this thread as well. I was looking at both cars (2015/2016 model years). I was looking for a semi-luxury car for a good price and the Azera and Cadenza kind of fit that bill. For me, I liked the exterior of the Azera more (even though it kind of looked like a Toyota Avalon), but the interior on the Azera didn't have a very upscale look to me. When I saw the Cadenza, it has a nice exterior look to it, and the interior looked miles ahead of the Azera for a luxury look. Or maybe I just like the look better.
As for the ride, I agree the Azera was a bit stiffer and noisier on the inside. I think the Azera runs on lower profile tires (which might aide in the preference for the exterior styling), which wouldn't help with the added road noise. And even though I think the Cadenza feels "loose", I'll probably try the "inexpensive" modifications to help in that area. I still like the ride quality though and quietness in the cabin. I put a higher priority on those qualities than feeling the road.
Another reason why I chose the Cadenza was for the rear seat leg room with my drivers seat in my position. The proportions of the car are done well. Some large cars (like the Taurus/MKS, E-class, etc) can't touch the back seat leg room in the Cadenza.
While the car is quiet, I find Kia could have done more with sound deadening. If you look in the Spare Tire wheel well under the trunk carpet (or anywhere under that carpet), there is very little to no sound deadening material. A quick and easy fix for this is to remove the spare and lay down Dynamat (or something similar), and it should quiet the back end of the car significantly (10dbs or more). But I have a feeling there is little sound deadening in various other places (someone did a write up showing the Cadenza's floor boards with the carpets removed). Which amazes me that the car is as quiet as it is.
All in all, if you can pick up a used one at a good price like I did, you'll be very happy with it. I enjoy driving it every day.