Tastidian's demonic horns, large scar, and pulsing blue just screams cool.
I picked Darkeye, because I am just a big fan of horns on shadowlings. I wish more shadowlings had horns like Tastidian and Darkeye. Also, the scar over one of Darkeye's eyes makes him seem like a veteran warrior.
The bandana covering half of Niven's face give the shadowlings a cool, outlaw look.