Carlman,
I'm in process of upgrading my stock audio system as well. I've done some reading with no real comparo. It's frustrating and tough to compare head units because they are demo'd in a dealer display, not in my car.

The three brands that keep coming up for SQ installs are
Nakamichi,
Denon,
and Eclipse.
Some recommend Alpine, etc, but most seem to like these three brands the best for SQ (though you do tend to lose out on some features).
I'll probably go with Eclipse. They have an interesting theft deterrance system that I am HOPING most experienced theives know about. You put in a CD (any audio CD), and that CD becomes the master CD for the system. Once the deck loses power (i.e., it's been removed from the dash, the battery is disconnected, etc), you will have to re-insert your master CD to bring the deck back to life. Only you, the owner, knows which CD is the master CD. If I go Eclipse, I intend to keep my master CD in the house, not in the car.
Anyone know about this security system? Is there a way for a wiley theif to circumvent it?
Regards,
John G