The big difference in the two would be the radial corallites, they are hard to see from the picture. Also A. humilis will have the dome tips.
Acropora torresiana will have "Radial corallites are short and tubular, of uniform size and are neatly arranged in rows down the sides of branches."
Acropora humilis will have "Radial corallites are of two sizes, the larger are usually in rows and have thick walls and only slightly increase in size down the sides of branches."
If the radial corallites flare upward into a pocket shape then check out Acropora digitifera.
http://coral.aims.gov.au/factsheet.jsp?speciesCode=0023