Excellent answers! One additional point is that Frodo, alone of all the ringbearers, was given the ring of free will. He did not acquire the ring by cheating or murder.
Frodo and Gandalf, in the chapter The Shadow of the Past, discuss how Gollum could not give up the ring, where Bilbo did:
‘What do you mean?’ said Frodo. ‘Surely the Ring was his Precious and the only thing he cared for? But if he hated it, why didn’t he get rid of it, or go away and leave it?’
‘You ought to begin to understand, Frodo, after all you have heard,’ said Gandalf. ‘He hated it and loved it, as he hated and loved himself. He could not get rid of it. He had no will left in the matter.
‘A Ring of Power looks after itself, Frodo. It may slip off treacherously, but its keeper never abandons it. At most he plays with the idea of handing it on to someone else’s care – and that only at an early stage, when it first begins to grip. But as far as I know Bilbo alone in history has ever gone beyond playing, and really done it. He needed all my help, too. And even so he would never have just forsaken it, or cast it aside. It was not Gollum, Frodo, but the Ring itself that decided things. The Ring left him.’
