As I see it:
------------
If they started a reasonable distance away, Garak would win via subterfuge probably without ever seeing Han in person, and make it look like Luke did it
In a western-style shootout, assuming both are present with only a hand weapon, they'd both die from pre-tenth-step shots.
In a walk-in-the-room face-to-face and unexpected-need-to-kill situation, Han would probably be the faster draw.