Can quite happily confirm the Pioneer 77mp is the best head unit out there for SQ(well for under £400 smackers anyway!) i had one for a while then like a muppet i replaced it with a Jvc avx1 dvd unit, and the sq was nowhere near as good, i also had an alpine 7893 until it got nicked, again that was a good unit, but with the wrong speakers the top end was very harsh.
Blaupunkt are also very good for SQ the looks arent to everyones taste tho, for me in the £300 range, pioneer are tops,closely followed by alpine and then blaupunkt. Kenwood,clarion and sony just look tacky and maxpowerish to me.
One think some of you experts might be able to confirm for me tho, how good a sound source is the ipod? (in terms of SQ) my focus ST comes with a double din sony unit which has AUX in, now im loath to change the HU as its meant to be quite (despite what i said earlier) and it has a 6cd changer,steering remote all connected and at the mo there arent any adaptors,it also looks very good in the dash and none of the facia plates are much kop for the focus. So im thinking of keeping the stock HU in and add in an amp and front components and some RE8`s in the boot, and using the Ipod as the main sound source, what do ya reckon.