The two principle pluses with 100% carbon masts is that they are notably lighter and they offer far quicker/livelier reflex response. These factors maximize a sail's performance responding to the gusts, thereby offering optimum power and drive while letting the sail breathe to the best of its ability.
The distinct advantage that an RDM has over an SDM is a greater durability in a surf environment due to its greater wall thickness. However, that's not to say that an RDM offers better performance characteristics. The two distinct mast types do offer subtle differences even if they have the exact same bend curve, and that's related to the differing overall shape of the tube structures.
What's the best? That's hard to say because folks have different personal preferences. Also, much depends on the type of sails being used, to include the intent and focus of the sail's designer. Needless to say, it's best to use the mast type/brand specified by the designer.
Overall, if you can afford it, always go for the highest carbon content, regardless whether it's an RDM or SDM.