Dugtrio is the fastest SR setter and can trap Magic Bounce users for a guaranteed SR, while Mamo is immune to Taunt and thus isn't as vulnerable to faster taunters like Prankster Sableye or Weavile. Overall, I'd go with Duggy almost always. Trapping allows a smooth switch into Cinderace on a mon that usually doesn't have Taunt so u can gurantee the Court Change. Mamo can set up on Weavile sure but when you switch into Cinderace then you're just getting taunted anyways.Would Dugtrio or Mamoswine be the better Stealth Rock setter in a non-NatDex Court Change team? I believe they're the two best SR setters in the non-NatDex meta because Dugtrio is the fastest and has Arena Trap, while Mamoswine is the fastest setter with Oblivious (and is neutral to SR, while Dugtrio resists). Mamoswine scouts for anti-Court Change tactics more poorly, though.
Gen8 Sets:
Below is a list of sets with descriptions on how to use a good majority of viable mons currently found:
https://pokepast.es/a7f765de1a8d92e9
https://pokepast.es/7780113ea83c6cb2
https://pokepast.es/07b12bb090e8fe20
https://pokepast.es/52bb1e51cfb81f26
https://pokepast.es/e16064dad2d4a6d3
https://pokepast.es/b0f72fbc978f6b68
https://pokepast.es/b1f637ff60e1bbb6
https://pokepast.es/4d3409289d7c035a
https://pokepast.es/47bbde28b614fbb9
https://pokepast.es/32fb63a6e1cf6714
https://pokepast.es/c4b813c9cbba31f7
https://pokepast.es/ee3c16240e0e9e97
https://pokepast.es/12e084b2f769a5d8
https://pokepast.es/ffecf5657ad67f6c
https://pokepast.es/d87858c7f967baab
https://pokepast.es/ae99a742c2808b3b
https://pokepast.es/ec89e8fe63b16c7f
https://pokepast.es/04e7dccd5f1c4c4d
https://pokepast.es/c60e6baa8a869f14
https://pokepast.es/1a5836ecc45fc7bc
https://pokepast.es/4ca7d0ac718efaf3