To me, this sounds like it necessitates consistency over all else. So look for a deck that provides that. Probably should away from most stage 2 decks. I hear people say that Zoroark/Golisopod is top notch for consistency, but I've never been able to make that deck click for me.
I'd lean toward something with a focus on basics... So to mean that's Buzzwole, Volc & Friends, or Lapras.
Sidenote: how far do you tend to have to travel for ARGs? I'm thinking about trying them next season, but none are in my state.