Greatest warrior?
Hmm... hum... (no, not Treebeard
)... The range is indeed quite wide. I am sure there is somewhere mentioned who was considered the strongest, at least of some time... that can help us...
But the people I can think of now are
Húrin,
Túrin,
Fingolfin... maybe even
Fingon... I'd say someone among these. I will maybe even go more for one of the Men than for one of the Elves... short-lived but maybe... well, what do you mean by "greatest"? If it also means "famous", then the short-living are in certain disadvantage... but then I'd say
Fingolfin. I can't think of anyone else who fought (and hurt!) a Vala (except for Finwë in self-defense, and he just fought, not hurt).