Without knowing more details of what boat/drives you've got it's difficult to get into the details. I can say that Bravo 1's on my '88 312 are RH (normal) rotation on the starboard and LH rotation on the port. With that said, years ago I had a Wellcraft Nova 250 and both were RH rotation with no perceived difference from other boats that had counter-rotating (RH/LH) drives.
It is my understanding that having counter rotating drives is crucial with high horsepower and high drive mounting (on the transom) applications. The less wetted surface at speed (hull in contact with the water) the more the counter rotation helps to stabilize the craft. IMO if your boat has less than 500HP each, I wouldn't spend any extra money on getting a LH drive. If it's the same money, go for it!