I have done all 3. I found UPS hubs to be the easiest, but it’s also closer to me. I have yet to have an issue with either, but my UPS hub is just friendlier… esp once I announce it’s a firearm.
Alot of pressure being put on shipping companies. Call and make sure your data/info is good. If item is going to the OEM there is less red tape. Anyone who is not the shipping company is a no go (eg UPS store, or whatever).
Tell your smith to email you a copy of his FFL print it out and make two copies, you tracking thus far ? Put one copy in the box with your barreled action and a note with a copy of your DL and all contact info cell phone email address etc..
When you go to UPS or FED Ex show them a Copy of the Smith's FFL and tell them you are shipping it to him or her for repair. If for what ever reason you get a Dummy helping you and you get some blow back ask for the manager or Supervisor they should handle it with zero issues...