Opponents In This Location
Rock Club Member Matthew - Hard Pokémon Deck
Rock Club Member Ryan - Excavation Deck
Rock Club Member Andrew - Blistering Pokémon Deck
Rock Club Leader Gene - Rock Crusher Deck
(After talking to Leader Mitch at the Fighting Club)
Fighting Club Member Chris - Muscles For Brains Deck
Guide
The Rock Club is a great place to start your adventure no matter what deck you have, since Gene is the only Club Leader you can duel without any prerequisites. Rock doesn't have its own unique energy (Rock, Ground, and Fighting types are all grouped under Fighting Energy), so you'll find that like Brock before them in Pokémon Red and Blue these guys use a mix of Rock and Ground types, with a few others thrown in for good measure. Matthew and Chris can be found in the Club Lobby (Chris, only after talking to Mitch by going to the Fighting Club), the room to the left of the entrance. Andrew, Ryan, and Gene are all in the main room of the Club.
All of the starting decks should have an equal chance here, since you're not going to be relying heavily on Normal / Colorless cards. If you're looking to hit weaknesses, though, you should try the Bulbasaur & Friends Deck, as some cards included in every deck here are weak to Grass-Energy Pokémon. Just don't bring an Electric-heavy deck in here once you start experimenting, unless you like a serious challenge. Even Surfing Pikachu is still a Lightning-Type, after all.