I know Meryl Streep most often gets tagged with that title, and she has all the Oscar nominations, and is truly great, but I just don't think anyone else could have pulled off what McDormand did in "Three Billboards."While she's not nearly as prolific in terms of roles she takes, I don't think I've ever seen her give a bad performance.
Obviously, "best" is subjective, and there are so many worthy people. Just wanted to shout out how good she is, both in "Three Billboards" and generally.