The best meat is a very subjective concept.
I haven't personally eaten cemani but we have processed a few silkies and silkie mixes which are also black skinned. Silkie meat is thought of as medicinal and a delicacy in some cultures but I can't say as we've so far noticed a difference. The next time we have it I plan to cook both a black skinned pure silkie and a white or yellow skinned bird a rock or an Orpington. As of this point we haven't yet eaten a pure silkie only a mix.
Also I can't say I've been too impressed with the Plymouth Rock meat. The best meat we've had so far has been from the Orpingtons and the EE. We've also had some very meaty legbar Orpington mixes.
Note our rocks were hatchery barred and whites while our Orpingtons are all English with just a few Americans left.
I haven't gotten the chance to try Bresse but hear amazing things.
We've also tried hatchery cuckoo marans, and a number of other breeds.