[HummerNewbie]

It really depends on what you want from the system. I would not waste the money on the factory NAV especially if you plan on replacing it with an aftermarket unit. Get the system that best fits your expectation sound wise. For me it was the Monsoon system and anything less would have been replaced within a week but it really depends on what you want out of the system. If you are like me and have never left a factory system in a vehicle then only the Monsoon might cut it and start from there. If the Monsoon isn't enough, get a base system since you are going to turn around and take it out anyway. The aftermarket NAV system will hook up to any of them with the correct wiring harness. Hope that didn't confuse you more.