My best horror authors ever and best authors ever would be two different lists. But here are some of my favorite horror writers:

Poe
HPL
Clark Ashton Smith
William Hope Hodgson
M.P. Shiel (haven't read much, but he's off to a good start)
Arthur Machen
Thomas Ligotti
T.E.D. Klein
Algernon Blackwood (seems he wrote too much but I love some of his tales)

Brian McNaughton's THRONE OF BONES is one of my all-time favorite contemporary horror titles.

etc.
etc.