Joker is one of the more complicated Phantom Thieves to choose Pokemon for. Ryuji's team is a lot easier to put together. His Persona's element is electricity, so naturally, he'd be an Electric-type Gym Leader.
He's an outspoken, energetic guy whose affinity for electricity makes perfect sense. He's quick to take action, with an act first, ask questions later kind of personality. Oh, and he's also a former track athlete.
Factoring in all of those facts, here's what his team would be: