Sync. The first thing you'll notice is Pioneer's pixy-dusted UI which easily trumps the Sync's rather staid presentation. The videos show off Pioneer's real-time data feeds and natural speech recognition with the help of some smarmy actor-slash-models who'll probably be serving you lunch today if you live in LA. But we digress. Videos after the break... which, let's be honest, is the best we can do until the DivX-happy, SD-friendly AVIC-F900BT, F700BT, and F500BT (pictured) are released in June.
Update: Just heard from Microsoft. Turns out that the AVIC-F series runs on the Microsoft Windows Automotive OS -- the same core as Sync.