I am familiar with regularly using three different factory equipment in dash systems.
A BMW 2001 M5, that I upgraded to factory DVD unit, A 2004 Porsche Cayenne S DVD Unit, and the Commander Factory Unit.
The BMW and Porsche factory units are quicker and easier to input destinations, due to the controls they use. I think the Jeep adds a confirmation/enter step that is slightly annoying.
But the Commander unit, once in operation, seems to be fairly accurate, and is a pleasure to use. Once destinations are input, I would say it is better than the BMW unit, and equal to or better than the Porsche unit. The Commander unit is slow to load at start, but I added a Clifford Remote Engine Start and Alarm, which helps, so it's essentially ready to go when I am ready.
One thing that is unfortunate, is that you cannot utilize all destination input features if the vehicle is in motion. You can perform limited input to destinations that are already in the memory. The screen is a good size, and the features are about everything I need to get from place to place. I use navigation frequently, as I work in the real estate industry. The BMW and Porsche, on my model year vehicles, allow inputs while the car is in motion. Helpful if a passenger is doing the input.
'06 Commander Ltd, 5.7L Hemi, QDII, Midnight Blue, Gibson Exhaust, Raingler Net, K&N FIPK, Remote Start, Optima Yellow, Skid plates & Tow Hooks, Rocky Road 2.25 Lift, New Rear DT Shocks, 265/70R17 REVO's, 6061-T6 Custom Wheel Adapters, 4xGuard Rock Rails/Steps
'05 Land Rover LR3 SE
My wife has a Nissan quest with a nav system, and I have it in the commander. If I had to pick which was better, I would probably go with the Nissan, although that doesn't mean that the Commander's system is bad. There are a couple little things in the commander that I noticed...
When I enter my home address as a destination, it points me to the correct street but not very close to my actual house. When I'm sitting in my driveway, the system tells me that I'm 2/10ths of a mile away from home. It makes me wonder if other addresses will also be slightly off.
As Sycohemi mentioned, there is an "extra step" in the commander system. No big deal, but you have to push three buttons just to get to the map with no destination.
My third issue is that you have to enter an address as a destination before you can put it into your address book or edit your address book. This is related to the previous point - it's an extra step. In the Nissan, there is an option to go right in and edit your address book from the main setup screen.
Lastly, there is no option to "save current location" to the address book. At least I cannot figure it out if there is. This is nice to have when the system is telling me that my home is down the street. If I could just tell it to save the current map location as my home address, it would aleviate that little issue. The Nissan has this option.
Othere than those minor issues, the system is easy to learn and easy to use. The voice guidance in the commander is better than the Nissan, but that's just a preference. I still think it is worth it to get the Nav system, even with its quirks. In addition, having that Nav screen gives you a much nicer interface for the stereo, particularly the satellite radio display of song and channel information that you don't get on the non-nav system.