The SG2 provides a bit more info (can display 4 gauges at once), but I think I prefer the SGe for its "progress graph" that does a live chart, updated every minute, of your fuel economy relative to your average since last reset. Customizable too (you can set the graph's midpoint to be a goal, and I think the time per bar is customizable).
I find the graph to be very motivating.
From:
ScanGauge-E Review and Comparison