In an FF, FR, MR, and RR cars 400hp and under, I floor it from the start.
With an FF, FR, MR, and RR cars over 400hp, I rev up to around 75 ~ 85% throttle. If the tires slip when the lights go green, I maintain throttle pressure until I hear the revs drop as the tires start to hook up, then I floor it.
If I'm in a 4WD, I floor it -- horsepower be damned.
Results online have been fruitful.