They were both loners who took everything upon themselves; neither would make a great leader. I would vote Itachi though because he was caring, empathetic, and quiet. Obito was always blabbering on about his ideologies and manipulating people. Shinobi in Konoha would have followed Itachi if it hadn't been for the Uchiha massacre. Even members of Akatsuki looked up to him and respected him. Now, if you mean young Obito before he went AWOL that would be a tougher call. Young Obito was very caring, passionate, and charismatic.