A recent study by Dr Jim Martin showed that crank length makes pretty much no difference in terms of power production.
Where it can make a difference is in comfort and position of body. Shorter cranks can allow the body to go lower at the front and hence more aero.
FWIW, I use three difference cranks lengths (167.5, 170 and 172.5). No difference in power, performance or comfort.
So if anything perhaps err on the side of shorter.