It is clearly closest to DAO as the trigger draws the firing pin back prior to release. The Glock firing pin, when at rest, is not in its fully down position, but partially back, held there by the lug of the firing pin resting against the rear leg of the cruciform.
Striker fired pistols fall into three categories: (1) firing pin fully down and trigger pulls it all the way back before release; (2) firing pin partially back and trigger pulls it the rest of the way back before release; and, (3) firing pin is fully back, and pulling the trigger merely releases the firing pin to fly forward.
S&W Sigma, SW9VE, SD9 are type 1.
GLOCK is type 2.
S&W M&P, Springfield XD Series, etc., are type 3.