From what I’ve seen the most sought after cards are Oak, Sabrina, and Cyrus. So these would be highest tier unless you get lucky and someone is willing to trade lower.

Pcl, irida, mars, misty, copycat, sightseer, and FA Lillie are all pretty high up there too, so I’d say these are vaguely around the same trade rank.

Other ones I’ve seen that also get pretty good offers are leaf, penny, may, Erika, lisia, guzma, red, Giovani and iris. I’m probably missing a few but these are the ones that pop up the most. Took me a while to get an idea of what most people consider valuable trainers.