I have the Clarion DRZ 9255, fantastic unit, had it since July 2004 and its working great since. It is a VERY simple headunit. ONE LINE display that shows very basic stuff. The menus take a bit to get used to, but the unit does everything and sounds great. The face DOES NOT detach, but most people that I have shown this HU to have all said the same thing "This thing retails for $1400? It looks so simple", I don't think it will really attract a thief.
As far as money goes, if you are trying to save a little cash but still want a great headunit, I think the Eclipse CD8053 is about the nicest out there for the money. Great sounding unit, tons of features, just can't say anything bad about this unit.
I can't speak for the Pioneer and Alpine's since I have never used them, but there isn't a single HU out there that I would trade my 9255 for (even the F#1 Status from Alpine).