i have a kenwood kdc mp532u. i really like it, although i did have a display issue with this my unit - fortunately under the factory warranty(which they extended a month for me) it was fixed.
i got it for the USB feature and since getting this unit i dont think ive burnt any cdr's(for the last year).
i dont think this model is available anymore but i like it for the most part. im not sure about the other brands but a usb feature that you may want to check on is whether your usb mp3 files will continue to play from where you left off if you remove the flash drive or turn on and off your car. they probly do, but before i got my kenwood i tried a cheap usb stereo from some off brand that would not function in that way (really annoying if you like listening to podcast mp3's).
also be aware that some flash drives might not work with your HeadUnit. i use pony flash drives, they're cheap and work well.