There are 36 reviews for one of them, and 17 reviews for other one on crutchfield. This is where I suggest that you look. If one or two people come here, it is no comparison to 53 owners.
Most of the bad reviews with these units is the install. If anyone expects a loudness button to solve volume problems, they are mistaken. Loud volume with the loudness button pressed is going to sound horrible.
If someone doesn't have their speakers connected properly and not in phase, it is not going to sound good. It doesn't matter what headunit you have. If your balance to the right gives you sound on the left, it has nothing to do with the headunit. These are the problems that I see with the bad reviews. And, they are bad installs, and even a "professional" installer can do bad installs. I had that problem myself. They just put these things in and they don't really care about perfection. You have to really hound them sometimes or just fix it yourself.
Then, there are people who complain about getting a defective unit. The manufacturer can not be responsible if the box is beaten up and you get a broken product because of bad handling or shipping. Again, I see those problems too with the bad reviews. This is not a fault of the product.
Then, there are people who are not good technically and complain that the headunit is too complicated. Then, they should not have a high tech Headunit. Both products are high tech units.
Then, there are people who complain about no bass or bad bass from the speakers. Again, this has nothing to do with the headunit. People complain about the bass boost being bad, but bass boost is not going to be good with midrange speakers, and probably not designed for subwoofer speakers, unless you have low frequency pass. This could also be a problem with how the music levels were set during the recording. If the gains were set too high during the recording, it is not going to sound good with even more gain in the bass, or at loud volumes.
Then, there are people who complain that the unit doesn't start up right, when they start up their vehicles, and it freezes. I
never leave my high tech electronics on, when I start my vehicle. The headunit gets increasing and decreasing electrical power during start up because the starter takes a lot of the power. This can cause the unit to boot up badly, and it can short out. Eventually you will probably destroy the unit this way. It's like you get a power surge or power fluctuations and your computer freezes. You have to turn off your computer and restart it, and hope it still works properly. No vehicles that I know of have surge protection for the radios.
These are the things to consider when you read the bad reviews.
Pioneer AVH-4000NEX DVD receiver at Crutchfield.com
Pioneer SPH-DA120 AppRadio 4 Smartphone receiver at Crutchfield.com