For me, it came down to knowing myself. From a feature set standpoint, the factory NAV and after market ones are pretty close, but you have to disconnect and stow the aftermarket ones each time you park or risk tempting a thief. I know I would consider that too much of a pain after a while and it would end up spending a lot of time in the glove box, so I got the factory NAV and I use it all the time. The factory NAV also has a few features that the after market ones don't, like adjusting the color scheme to a darker set when you turn on the headlights (nighttime mode), displaying audio info on the same screen including folder navigation/display for my MP3's, lots of PHYSICAL controls (rocker switch for zoom, joystick for scrolling and panning, etc.) which I find much more ergonomic than pure touchscreen, ability to use the steering wheel controls, etc. I don't regret it at all. I also read that the NAV system runs on top of WindowsCE, and the software is on the NAV DVD, so eventually I might start experimenting with the hacks that are out there