Hi,
Brawling skill (Harp Core pg 35) says Brawling uses Tiny or Small attack on the relevant table.
I'd use Crush myself, but Impact may be more suitable - depends on your style.
Since Impact does a bit more damage, I'd probably go for Tiny Impact Criticals, but then again we discuss rule changes amongst our group and I can see some people wanting to make it more even by having a small Crush, or even a Tiny Crush.
But thats where the rule is!