Tough call. There are so manny to choose from:
O'Reilly (most consistent armor deco in the game),
Poluski (best scar),
Klassen (most- fan appeasing),
Garnet (both one of the most prolific and the most ethnically diverse [he's green]),
Dags (shootiest cripple)
And of course they all leave without being activly annoying or making you wish you were dead.
Speciall mention to Ruiz for being the only speeking part (Poluski's line in the intro doesnt count because he then becomes a mute) which doesnt result in hair loss or nausea.