What is the most accurate coordinate system for calculating areas of polygons?
I'm currently involved in comparing the "official metropolitan" areas of several cities against their actual overall urban footprint. The official metro areas' areas can be found in other sources, but I need to get the most recent urban footprint area.
I've found the fastest way to do this is to draw a polygon in Google Earth around a city's urban sprawl. As I want to create an explanatory graphic, I then brought my GE polygon into ArcGIS 10, where I converted it from KMZ to layer, and then saved the layer data as a new feature class in my specific city/map geodatabase.
Now, out of habit, b/c I'm focusing on a specific small area, I'm projecting things in UTM. I checked the attribute of my new "urban footprint" feature class polygon and found there to be an ~600,000m2 difference between the polygon area in Arc and the same polygon's area given in Google Earth.
In light of this, my question is which area value is more accurate and should I use in future calculations I'm going to do?