Testing and comparing GPS modules is a tedious process because claims often vary greatly from actual performance. Thankfully, our friends at Sparkfun have done the work for the ones that they carry -Sparkfun GPS Tutorial. After reviewing the information they found, I decided to use the Copernicus II because it consistently had the most accurate results.
NOTE: This GPS technology has the correct amount of accuracy for farms or people with yards over 1 acre. In order to be accurate enough for most city yards, RTK GPS technology would be necessary. The cost for such technology has dropped significantly in recent times, but it is still expensive relative to the WAAS GPS of the Copernicus II and at the time was not necessary for my needs. WAAS GPS technology was developed for landing aircraft in the USA without having a visual of the runway and is fairly accurate.
RTK Accuracy: Plus or Minus 2-3 centimeters XYZ
WAAS GPS Accuracy: Plus or Minus 1-2 meters in XY and Plus or Minus 2-3 meters in Z