I do my own work, but I am not my favorite gunsmith, just the cheapest I can find.
Now, when I think custom gunsmith, I think of Martin Hagn, Butch Searcy, Steve Earle, or Dewey Vicknair to name a few. But they do very different work than most other suggestions here.
Stuart Satterlee would fit in both categories of custom one off work (he makes his own actions), or precision rifle builds.
Jeremy