[akhtene]

To my mind Aragorn was just the perfect man to do what he was doing. He had the right (by birth) to lead men and elves, being a descendant of a glorious house. He got necessary training and knowledge in Rivendell and during his wonderings and military campaigns. And he’s got a definite aim, which can’t be diminished by having some personal motivation. He just knows what to do, how to do it and that there’s no-one around to do it better. Note how he always appears at the time he is most needed – at Bree, leading the fleet by Anduin, in Minas Tirith to heal Faramir and Eowyn.

Just imho I don't see anyone claiming Aragorn's responsibility. Gandalf is preoccupied with too many matters at once, and for part of the time outof action. As for Gimli and Legolas, I somehow see them as just observes for their races, watching that everything is done right. They allow themselves to be led, perhaps not having a motivation as strong as Aragorn’s. (Sorry if I Have misinterpreted things)

However strange it may seem, if I had to compare Aragorn and any other character, my choice would be Sam. They share that determination to do all that is in their power (and above it) and finding strength for it.
The teams Gandalf&Aragorn and Frodo&Sam have something in common. Gandalf has his restrictions; Frodo’s Burden is too heavy for him. But for Aragorn and Sam the Task could have never been completed. And Sam is quite a pain in the neck at times, hehe.