I bought the 880 because it has two knobs which is way easier to use than one multi-purpose awkward knob. If its not easy to navigate, it sucks. Two knobs makes this requirement satisfied.
Also, it looks super clean and classy compared the the 780 or 680. The pictures on the pioneer site don't do the 880 justice. It looks way better than that in person. And when the display lights slightly dim when your turn your headlights on, the deck looks soo sexy.
Thats why I bought the 880 over the others...