[Finwe]

I think that the Merry/Pippin team would have also worked. True, they seem so immature and unrealistic at times, but they are still young. Frodo and Sam are older than they are, and more mature. Merry and Pippin have an utterly selfless streak deep down inside them. Look what they did when it came to rescuing Eowyn and Faramir. Merry was practically reduced to a gibbering wreck from fear, but he still pulled himself together, and realized that something (or someone) that beautiful shouldn't die. He overcame the fear that reduced many of the greatest warriors on that field, and acted. That action saved the life of Eowyn, and helped slay the Witch-King.
In Gondor, when Pippin saw Denethor trying to kill himself and Faramir, the young Hobbit who felt so out of place in this big, wide world melted away, and a strong, hardened warrior emerged. He KNEW that Faramir was alive, and was going to live. He took the risk of being forever ostracized by Gondorians for deserting his post, and went to Gandalf and Beregond for help. Deep down inside his heart, he had that Hobbit-sense that told him that he could do something. That if he couldn't fight on both legs, then he would fight on one leg or reduced to fighting on both knees.
Separately, I don't think that either Merry or Pippin could have destroyed the Ring. They loved each other so much that they would have gone to Mt. Doom itself, by hook or by crook. True, they might not have left Gollum alive, and that would have posed a great obstacle to destroying the Ring.
If they had reached the Sammath Naur, and the Ring had corrupted Merry, then Pippin would have known what to do. If worst came to worst, and he knew that the Nazgul were approaching, then he would have tackled Merry and flung both of them into the heart of the volcano. And the same would have happened if Pippin would have been corrupted.
Merry and Pippin are different from the rest of the Fellowship in that deep down inside, they would risk their lives to ensure the quest's success. I think that scene in the movie where they use themselves as decoys illustrates that perfectly. It was an impulsive action, they both knew it, but they did what they had to do, and Frodo managed to escape. If it had not been for that, then the Ring would have fallen into the hands of the Uruk-hai, and eventually brought to Saruman, which would have been a disaster.
I agree with all those people who said that a Hobbit would be the only logical choice for a Ringbearer. That spark of courage deep in their hearts is something unique. No other race has it. True, they have their weaknesses, but it was that strength that ultimately prevailed.