I have personally owned one or two JVC units. They have been very high quality and sounded great. I have never owned Boss, but I think they follow the footsteps a Pyramid.
I have also had Panasonic, Emerson, and JBL.
Panasonic is just junk. Every Panasonic I have had I hated. The Emerson was an in-dash TV that got stolen. The JBL was a hell of a deal, that is why I got it. It had a 10 disk changer AND in-dash cassette for like $125.00. Sounded awesome and was very reliable.
Always wanted Alpine, but never wanted to spend the cash. I like the Pioneer, but could never find the deal or unit I really liked.
By far, the best I have ever heard was an ugly McIntosh unit. That thing was hideous, but it sure sounded like the angles were singing.
Tom