Ok lets analyze that:

Lance: probably. he’s been btfo’d twice and his team is not that impressive. one dragon, ice, or electric move and he’s in bad shape.
Steven: maybe. raihan has two fire types but almost every member of steven’s team has a rock or ground type move. toss up.
Wallace: absolutely not. between wallace’s type advantage, bulky team, and the ice type moves that they learn, raihan will be spectacularly btfo’d.
Cynthia: cynthia is cynthia so no. more in depth: milotic, garchomp, and togekiss will rape raihans team. spiritomb would probably put in some work too.
Alder: toss up. alder’s vanilluxe and druddigon are gonna do serious damage, but then again raihan’s torkoal, and turtonator can dispatch of the vanilluxe, excavilier, accelgor, and volcarona with ease.
Iris: iris without a doubt. every one of her mons can destroy raihan’s team. easy w.
Diantha: most likely diantha. she and raihan have some similar mons, but she has a mega gardevoir.
(You): idk depends on what team (you) have. For me, it was Mimikyu, Salamence, Decidueye, Florges, Aegislash, and Araquanid, so yeah i reckon i would win.