I haven't followed D D-Lewis that much apart from the excellent job he did in "My Left Foot"; I know his reputation is way up there. Whoever is "best", Duvall has to be on the short list. When you look at what he's done, going back at least to the original repugnant Frank Burns in the movie version of MASH, through Lonesome Dove, Tender Mercies, and how many more...
But I've also seen him turn up as an honored guest on the 700 club; I'd rather see him influence acting, not politics.