Well the Rubicon case (and most Jeep transfer cases) is a two speed, chain driven case with the option of 4 wheel high and 4 wheel low. The Atlas is an amazing gear driven t-case that has all the strengths of the CJ's Dana 300 with none of its faults. You can choose 4 high; 4 low; front low, rear neutral; rear low, front neutral; etc.
The Rubicon case has a 4:1 low ratio and a standard 1:1 high ratio, while the Atlas has various choices for the low ratio plus the standard 1:1 high ratio. The one pictured above was built with a 3:01 low ratio.