Assuming both are US Spec, they are very similar to each other. Major difference, visually, are the turbine wheels (91) versus throwing star (93), aerodynamic mirrors, M dorr handles, and door sillls. Mechanically speaking, 92 models have a 3.73 final drive versus 3.91. Clutch is ligher ont he 93s. In the case of Euro spec car, from '92 on, the engine changed to a 3.8L versus 3.5L (340hp vs. 310). Hope this helped.

Gus has it down except I don't see the 'shadowline trim' mentioned. 91s used chrome around the doors/windows whereas the 'shadowline' is black trim. As noted the major mechanical changes were the 3.73 rear end and the lighter clutch (both of which I don't think I care for, so why did I get a 93....? Never mind, just mumbling to myself....)