First of all, I don't prefer any brand. I'm all about function, quality, and value. Whatever brand offers me the most of what I want gets my dollars.
I have a Blaupunkt MP3000. It's great. I love it to the full extent that one could actually love a car stereo. MP3 track switching is super fast (always under 1 second to manually change folders/tracks, and about 1/4 second if it's just playing through to the next track), and it's so easy to operate, even while you're going 100 MPH (OK not that fast, but some models are annoyingly and even dangerously complex).
The only problem is that the display is really, really, really bright at night (this is only a problem on really dark rural roads, and you can work around it by just flipping the face plate down unless you're actually pressing a button or turning the knob - it continues to play when you flip down the faceplate).
For the price, it's wonderful, a great bargain, really. I don't understand why it doesn't get so much more internet lovin'.
There were some early complaints about "noisy" MP3 playback, but that has been fixed with a firmware revision for well over a year now. (In other words, if I don't hear a defect in an MP3 in Winamp, I won't hear it on this MP3 player.)
The Blaupunkt San Jose is similar, so if you're going to use amps, that would be a good choice because it has more line-outputs.
If you order from Crutchfield, you get all of the dashboard and wiring harness adapters you need, plus customized instructions for your vehicle, for no additional charge, and they don't gouge too badly on shipping.