I have an the Pioneer Avic-Z2 in my truck and just installed the Kenwood DNX-8120 in a friend's truck. I'd go with the Kenwood hands down. It's an awesome radio. The Pioneer does has prettier menus and maps, but the Kenwood has MUCH better nav accuracy and functionality, great bluetooth, awesome Ipod control, and capability of playing music and videos off a USB drive. It also has infinitely adjustable background colors and key illumination.
If I didn't already have $1000 worth of Pioneer accessories, I'd replace my Z2 in a second.