There are only two companies in the world that actually make the maps.
Tele Atlas - owned by Tom Tom (the GPS unit guys) and Navteq - owned by Nokia (the cell phone guys) who out-bid Garmin.
http://en.wikipedia.org/wiki/Tele_Atlas
http://en.wikipedia.org/wiki/NAVTEQ
So, as far as getting lost, you only have two choices. Some units can accept updated maps (typically cheap units can not.)
I have a cheap unit from Magellin and in my wife's car is a cheap unit from Garmin. The biggest difference seems to be user interface - the actuall key strokes that it takes to complete your task.
Personally, I do not like the type that announce street names since they tend to be real "chatty", talking all the time and most of the time they pronounce the street name wrong anyway.
Fun stuff:
I too use mine for business travel. I like the small ones that you can slip in to a back pack. While on the plane and seated in a window seat I took mine out and got it to sync up. Over Iowa, I could see that we were headed over Chicago next, Lake Michigan, Detroit, Canada, south over Lake Erie and landed in Cleveland. It made for a fun hour. Keep in mind, the inflight magazine had GPS units listed as forbidden devices. I suspect that just dont really want you to know where your at - terroism, parchuting, etc.
While in the plane and playing with the features on the GPS, I set it to find directions home. The unit flashed repetedly and then just shut down.
In order to get directions it first needs to find a street level starting position and at airplane speeds it could not find a strart.
The coolest part is now in the data section on my GPS unit my maximum top speed is 572 mph!