I would choose DIN because most tonearm cables are offered in DIN to RCA. If you choose RCA that doesn’t enable you using any interconnect. Low capacitance, low impedance and proper shielding is necessary. You need to find a RCA to RCA tonearm cable which limits choices.
Directionality of a ground wire? What does it mean?
To the OP question: I'd choose the MDIN connector. It is a better connector for a true differential signal path to the sut or phono amp than the (quite horrible, why on earth did it become a standard) RCA.
Ground wire, or wires, used for grounding purposes, have to be checked for directionality, as the direction in which the wire is being connected - from the source component to the ground destination - can greatly affect soundstaging and frequency extension at either ends.
