All things being equal, barrel length has very little affect on accuracy. Especially when as little as 1/2" or 3/4" is considered. The difference between two barrels of the same length will often vary more than two of different lengths.
In the handgun, sight radius does affect accuracy. Since this is usually determined by barrel/slide length, the longer usually gets the better accuracy.
But, what kind of accuracy are you talking about? One half inch groups at twenty five yards? Twelve inches at a hundred? Or face to face?
Up close and personal, accuracy is not that much of a consideration.