For me, I think it ... everything. Hard to pick one over the other. But blacked out taillights make a HUGE difference from the back.

mirror assembly, mirror covers and window trim have the biggest impact from the side (though roof extention looks sportier as well).

cant really notice the front eyelids, but definately can notice the LUX V3 white eyes, and my grill and grill surround are distinctive.

The lest important are the things I've done to the interior, like the gas/brake pedals and mats, etc.