>>38668013Nate/Rosa since they beat every single gym leader, champion (prior to Gen 5), and Red and Blue at the Pokemon World Tournament.
Other than that, I'd say N as he has a legendary dragon, Cynthia as a very powerful champion, Ethan/Lyra as they take down two Pokemon leagues and defeat both Red and Blue. I'm not sure who to put fifth, but maybe Steven as he is the final boss for Emerald after you beat the league.