I've got the DDX-419. SQ wise it's got most features you'd want and the 4v preamps make sure you don't have to compromise with your amps. I haven't had a chance to use the Pandora app - I think it only works with iPhones, and the navigation is "optional"/"ready" - you still have to buy the app, which has a non-trivial price tag. I'd say the biggest negative on the receiver is the bluetooth audio/telephony.
BT Audio streams well enough, but the data loses tons of fidelity on the way back out the stereo. Maybe I'm doing something wrong, but I've tried multiple smartphones and different mp3s and the result is always the same - very low definition sound. Better off using the USB port or AUX-in.
BT telephony has a REALLY NICE interface. Pairing is immediate and non-intrusive. The software side of this is really nice. Unfortunately, the mic kenwood uses is crap. Callers complain that I sound "very distant" - I've moved the mic from my rearview mirror to the A-pillar and if it improved it was negligible. I've tried looking for fixes, some people have even used the BT mic from pioneer receivers (which don't have this problem) but found no positive result.
Anyway, I love the receiver, just don't buy it if you're wanting a great Bluetooth experience - this is not a dealbreaker for me, as the SQ/cost far outstrips whatever utility I'd get from BT.
BTW, I've got mine setup with a sandisc cruzer fit
. 16GB for about $10, never really leaves the dash.