I had a JVC that was a step or two above the KD-R210. It sounded great if you didn't turn up the bass or run the volume very high. If you did both, you could only turn the volume up about 75% then this horrible popping sound would happen through the speakers. I took it back and tried another one that was another step up, it did the same exact thing.
Then I tried a pioneer that was around the same price at the time (2 years ago, $140) and it's sound was flat out hideous. I took it back and got another pioneer that was a step up in price and it sounded exactly the same, horrible.
Then I picked up a kenwood KDC-X692 and after a lot of tweaking, it sounded great and went almost 100% volume without cracking. Lasted a whole year, then just yesterday went belly up on me on my way home from work. Was running the volume around 75% and all of the sudden, it shut off. I thought maybe it overheated, so I tried it the next morning. Still dead. Pulled it and checked all contacts and fuses. Still dead.
Just got home from BB and picked up a Sony KD-R210. Sounded great in the store, had more features than a comparable kenwood and since my last kenwood died in a year, I was kind of looking at all of them. The pioneers still sound horrible and the JVC's still pop.
I don' run an amp and my car is a 06 Mercury Grand Marquis. I'm running Pioneer TS-A6973R speakers in the rear deck and front doors. They sounded pretty good with the kenwood and also in the store where I tried the Sony.