This is a highly debated topic and I honestly do not know the correct answer. Clearly if you accelerated too slow you would never get out of the lower gears and into your tallest gear so going too slow is clearly bad. OTOH I'm sure gassing it to the point of tire squeeling is also not a good way to get the best mileage. Somewhere in the middle must lie the truth. Personally I prefer medium to brisk just because really gentle acceleration is boring. It might depend on the car as well. Some of the best hypermilers swear by the really gentle acceleration technique.