The reason I go with Glorfindel, atleast over Gandalf the "grey," would be since Glorfindel's death I think he learned a lot. I believe what he says in The Council of Elrond to be quite accurate, although it's just suposition. Maybe, not necesarrily more then Gandalf the White, since I also believe Gandalf learned a lot from his death, and reincarnation, but it's just a matter of opinions
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You might be right about Treebeard, since he does "shut himself," into Fangorn, and for countless amounts of years stayed out of the wars, saying it was for Elves, Men and wizards. And he didn't have much care, besides for Fangorn, that could cast in some doubt. I take his knowledge about Saruman to be accurate, since he used to spend time with the guy
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