One of three: Free League, Monte Cook or Goodman Games. Free League because they produce product that WOTC, and anyone else for that matter, struggle to meet and on a consistent basis. Monte Cook for similar reasons and because the level of creativity and innovation is second to none.
Goodman? Hands down the highest quality adventures with the most creative stable of designers and the coolest game for fantasy on the shelves. DCC is visually different, exciting and evocative of a style of fantasy game that no one makes anymore, if anyone ever did, but was very much present in the old artwork from TSR and in the novels, films and other media that inspired D&D without being Tolkienated. It isn't generic fantasy. It also includes everything that 3.x had in elegant mechanics that are simple and easy to understand. The entire adventure line up is pretty epic and comes the closest to emulating not just classic D&D but also Moorcock, Lieber, Vance and Wellman perfectly. While the adventures can hinge on a gimmick the designers make the gimmicks work. DCC 100 is a peak example of that along with The Chained Coffin and The One Who Watches from Below. Sailors on the Starless Sea is up there with Keep on the Borderlands or Village of Hommlet as the greatest starter adventure of any version of D&D. Goodman just "gets" what makes D&D great, something I think WOTC kind of slipped the last couple years and I am not talking about the nonsense most people complain about, I think WOTC is too slick, too clean in presentation. D&D needs some warts.
Honorable Mention: Necrotic Gnome for the same reasons as Goodman.