I guess I jumped in too late, but here's my approach. I check the specs for the machines. Specifically, I check the
1. THD numbers. Lower distortion = higher quality sound reproduction.
2. Frequency response. The wider the range of sound reproduction, the more full & satisfying the sound will be.
I've seen dozens of people throw money away on super expensive car speakers that have a far narrower range of sound reproduction than the $58 Kenwoods I bought. They sound GREAT.
I have been buying JVC decks the last decade or so. Before that I was a Pioneer guy. I started shopping for a new deck for my RX-7 & the Pioneer units in my price range just didn't have the rich, quality sound I was used to. That's when I started crunching numbers to figure out what happened to Pioneer sound. JVC speakers were also top notch back then, but they're hard to find around here and their freqency response has trailed off in recent years.