Red and Cynthia are the two strongest (non-player) trainers in the mainline games, by the numbers. Cynthia's team is slightly higher average level, and has perfect IVs/EVs. But, if you want to argue lore, I'd say it's either N or Volo - the two trainers that have legendary pokemon on their team.
. 157 304 370 270 369 9 280 349 219
pokemon is red the strongest trainer
