I carry a Garmin eTrex Vista Cx and a simple Sunnto compass. With a 2 gb card, the Vista can hold City Navagator maps for the entire US in a handheld package. However, I can't look at the map page and the compass page at the same time while driving and the GPS does not get an accurate directional position while navigating until you have moved for several feet. Thus, I use the compass to dertermine the initial directionI need to head until the GPS "gets it bearings."

As others have pointed out, GPS units with electronic compasses (such as the eTrex), are very accurate, but alas, are dependent on batteries which can let you down at the worst possible moment.

So, for my money, there is no winner. The prudent thing to do is to carry both.

Craig.