In VGC MB, as far as I know, all the archetypes are at least somewhat viable. The only ones I haven't really seen are Bulky Offence and Hyper Offence (maybe they aren't prominent or maybe I'm just not recognising them). So, the main archetypes are:
- Weather (All weathers are good)
- Trick Room (basically all types)
- Setup (Normally with Mega Blastoise, Delphox, or Floette-E)
- Tailwind Offence (its never bad)
- Balance
And a mix of these also works, like SunRoom, Rain Balance, etc. Hope this helps!