Which GPS?

I have 2 TomToms and the MotionX on my iPhone. Both are equally good. Going the iPhone route it only down loads the maps necessary for the trip so you could if you deviate from your planned route and don't have phone coverage you could wind up without a map.

My brother has a Garmin and it is not as intuitive to use as the TomToms I have. Also, I forgot mine once when traveling and rented a Garmin and it's the only time that I actually found a mistake in the maps. It kept telling me to get off at an exit and when I did it would tell me I had gone the wrong way and couldn't recalculate an alternate route. Wound up asking for directions and once I took the correct exit everything was fine.

I suspect that no matter what brand you buy the map info all comes from the same place.