Quem foram os maiores arqueiros da Terra-média?

Elfos

O maior Elf bowman parece ser Duilin de Gondolin , um lorde elfo de Gondolin e chefe da Casa da Andorinha

Em seus " Contos Inacabados ", Tolkien refere-se especificamente a ele como sendo um soldado de bravura física impecável e tem essa dizer sobre suas habilidades com um arco;

Now the folk of the Swallow bore a fan of feathers on their helms, and they were arrayed in white and dark blue and in purple and black and showed an arrowhead on their shields. Their lord was Duilin, swiftest of all men to run and leap and surest of archers at a mark.

Beleg Cuthalion (AKA "Beleg, o Arqueiro", AKA "Beleg Strongbow") também é repetidamente chamado como sendo um excepcional arqueiro e possuindo a capacidade de disparar flechas grandes distâncias:

Moreover Beleg the Archer was great among the people of Doriath; he was strong, and enduring, and far-sighted in mind as well as eye, and at need he was valiant in battle, relying not only upon the swift arrows of his long bow, but also upon his great sword Anglachel (needed only by an archer because the orcs were so many). And ever the more did hatred grow in the heart of Mîm, who hated all Elves, as has been told, and who looked with a jealous eye on the love that Túrin bore to Beleg. _{^{The Children of Hurin}}

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Beleg: Elf of Doriath, a great archer; friend and companion of Túrin. Called Cúthalion ‘Strongbow’.

Dito isto, não há nenhuma razão específica para assumir que ele era o único grande elfo arqueiro.

Orc

Os orcs são invariavelmente descritos como uma porcaria com um arco, confiando na mera força de números e volume de flechas (envenenadas) para causar dano:

Behind them orc-archers crowded, sending a hail of darts against the bowmen on the walls. - _{^{LotR: TTT}}

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Dismayed the rammers let fall the trees and turned to fight; but the wall of their shields was broken as by a lightning-stroke, and they were swept away, hewn down, or cast over the Rock into the stony stream below. The orc-archers shot wildly and then fled. _{^{LotR: TTT}}

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But orc-arrows are plenty, and the sight of one would not be taken as a sign of Doom by Boromir of Gondor. _{^{LotR: TTT}}

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The orcs hindered by the mires that lay before the hills halted and poured their arrows into the defending ranks. - _{^{LotR: RotK}}

Para a questão bônus

Tilion. O guardião Maia da Lua.

...but Tilion was a hunter of the company of Oromë, and he had a silver bow

But Morgoth hated the new lights, and was for a while confounded by this unlooked-for stroke of the Valar. Then he assailed Tilion, sending spirits of shadow against him, and there was strife in Ilmen beneath the paths of the stars; but Tilion was victorious.

Eu não sei, Legolas fez descer um monte fantasma no escuro de um pequeno barco com um tiro no livro, se bem me lembro.