It depends on the person who Obito is fighting and on the latter's battle style. Defensive-wise potential - 1MS by far, for the fact that Obito in that form can simply outlast. And if even if he can't kill his opponent, Obito can still safely warp away anytime he desires, thus he can't be defeated. Offensive-wise I'd go with DMS, however, Obito himself just isnt that much of an aggresive/rushing type of fighter, so it would be of more use for him to go with 1MS, his overall potential would be better and the way he performs with 1MS. If only you cross out that blindness effect, due to overusage of DMS ( which is actually non-canon, Obito has never shown any signs of going blind. Yes, his eye did bleed once, but it was due to him having not enough chakra to teleport to a very far dimension, or simply because he was pushing his teleportation jutsu too far, thus it hurted his eyes ), then I would agree that DMS is superior.