I think it's striking that the more powerful characters know almost viscerally that they couldn't resist the temptation of
the ring.
Gandalf,
Elrond,
Galadriel (even though she is tempted) know what would happen to them if they took the ring.
The simpler characters (i.e. the
Hobbits, who have common sense but are not exactly Einsteins) are the ones who are affected less; I think
Frodo succumbs because he's being carrying it for so long and through some extremely stressful situations.
Maybe as
Aragorn grew in stature during the book his will to resist would actually decrease?
I definitely agree that being simple and having humility are the best ways to resist the Ring: when
Sam is tempted by it it's his plain
hobbit sense that saves him.
And as great a character as Aragorn is, he isn't exactly humble, is he? I think the Ring would tempt him in the same way as it tempted
Boromir: by telling him that accepting it is the only way to save
Minas Tirith.
Also, assuming that Aragorn captured
Gollum and forced him to show him the way, I don't think Aragorn would have tried the pass of
Cirith Ungol as he would know it's danger. Rather, I think, he would have followed
Faramir back to
Gondor after deciding that there was no way into
Mordor.
Also, while Aragorn is a lot wiser than Boromir, Boromir succumed to the Ring quite quickly without even having it on him. Imagine how fast the process would have been if Boromir was made Ringbearer. And in their desires Aragorn and Boromir really are quite simillar. Even though Aragorn is stronger than Boromir, I don't think he would have been able to resist anywhere near as long as Frodo.
Also note that fate (if fate you call it) seemed to favour Frodo in his quest: the
Orcs who had him captive ended up killing each other, the two orcs who were tracking him also had a fight, the
Nazgul didn't spot him and Sam found a road leading to Mount Doom while carrying Frodo. I wonder if it would have been the same for Aragorn.
Plus, as Olorgando mentioned, Gollum would not have been able to take the Ring from Aragorn if he managed to get that far, and therefore it would probably not have been destroyed in time.
All in all, because of his humility and posession of hidden strength I think Frodo is the only character who could have taken the Ring so far. Perhaps the
Valar even gave him these strengths so as to be able to resist it.