Both breeds are fine meat rabbits. Commercial rabbitries buy either. I happen to prefer New Zealands but that is personal preference. Florida Whites make a good meat rabbit too. They are a little smaller but they are very compact and produce a lot of edible meat for their size.
They're both excellent choices. They both have a good meat to bone ratio (small bones, big meat). I have New Zealands because that is what was available in my area and they are great. I think the Californians are prettier, but then maybe I'd have a harder time killing them.
What you want to ask a breeder is what criteria do they use to select their parent stock? My stock came from a long, long line of meat production rabbits who were carefully selected for good meat carcass, good mothering skills, fertility, large litters, easy breeding back, etc.. I have had no problems getting mine to perform. I am very happy with them.
I end up with so many rabbits, I usually sell half of them to pay for feed and eat the other half.
Having raised both breeds, I prefer New Zealands. I've had several lines of Californians, and they aren't as good mothers. I'm sure I just had bad luck with the breeders I had. I'm sure several people out there would disagree with me as they may have better lines than I did.
New Zealand Whites had the best temperaments, best mothers, biggest litters.
The meat from a NZ black will be a bit darker than a NZ white.