If Ninjutsu could damage obito+ theres no physical juubi i would go with Nagato as he can absorb all his ninjutsu whilst spamming shinra and other combos, Nagato has a decent chance if Obito is close because of Asura+Human path but he probably will lose.
Give him senjutsu he would win if the physical juubi isn't there and he would have to be able to run... if were talking about the current juubi and obito combination he would put up a fight but lose ... pretty hard.