[Maédhros]

Originally posted by The Saucepan Man
Even then, Sauron would have won, for the new bearer would have become corrupted by the Ring which was itself a part of Sauron. And, while that new bearer might be able to master the Ring sufficiently at first to usurp Sauron, he or she would surely eventually become subservient to its will. And then, assuming that it remained intact, Sauron would be able to return and reclaim it. The Ring, no doubt, would be only to glad to help him do so, and so the new bearer would not be able to rely on its power.

This is not entirely true.
From the Letters of JRRT: 246

Of the others only Gandalf might be expected to master him – being an emissary of the Powers and a creature of the same order, an immortal spirit taking a visible physical form. In the 'Mirror of Galadriel', 1381, it appears that Galadriel conceived of herself as capable of wielding the Ring and supplanting the Dark Lord. If so, so also were the other guardians of the Three, especially Elrond. But this is another matter. It was part of the essential deceit of the Ring to fill minds with imaginations of supreme power. But this the Great had well considered and had rejected, as is seen in Elrond's words at the Council. Galadriel's rejection of the temptation was founded upon previous thought and resolve. In any case Elrond or Galadriel would have proceeded in the policy now adopted by Sauron: they would have built up an empire with great and absolutely subservient generals and armies and engines of war, until they could challenge Sauron and destroy him by force. Confrontation of Sauron alone, unaided, self to self was not contemplated. One can imagine the scene in which Gandalf, say, was placed in such a position. It would be a delicate balance. On one side the true allegiance of the Ring to Sauron; on the other superior strength because Sauron was not actually in possession, and perhaps also because he was weakened by long corruption and expenditure of will in dominating inferiors. If Gandalf proved the victor, the result would have been for Sauron the same as the destruction of the Ring; for him it would have been destroyed, taken from him for ever. But the Ring and all its works would have endured. It would have been the master in the end.
Gandalf as Ring-Lord would have been far worse than Sauron. He would have remained 'righteous', but self-righteous. He would have continued to rule and order things for 'good', and the benefit of his subjects according to his wisdom (which was and would have remained great). 'Thus while Sauron multiplied [illegible word] evil, he left "good" clearly distinguishable from it. Gandalf would have made good detestable and seem evil.'

If Gandalf had been the victor of such a battle, Sauron would have been uterly lost.

Originally posted by Finwe
But what if someone of the calibre of Aragorn usurped the Ring? If Aragorn had taken the Ring, and become corrupted by it, he would have given Sauron some very serious competition. Perhaps someone with his strength would have been able to use the Ring to his own advantage.

ibid.
Until Sauron himself came. In any case a confrontation of Frodo and Sauron would soon have taken place, if the Ring was intact. Its result was inevitable. Frodo would have been utterly overthrown: crushed to dust, or preserved in torment as a gibbering slave. Sauron would not have feared the Ring! It was his own and under his will. Even from afar he had an effect upon it, to make it work for its return to himself. In his actual presence none but very few of equal stature could have hoped to withhold it from him. Of 'mortals' no one, not even Aragorn.

Not Aragorn. He would be no match.