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The usual: legendaries, sub legends, balltism base form pokemon, item trade-evos, shinies.
The thing is, some things like Mareanie, Dhelmise, Gible, Vulpix and Beldum are common as fuck now and in WT in their "popular" balls so they won't net you anything now. I haven't tried Castform or Vanillish but I'm pretty sure those aren't worth as much now.
Of the bankmons Kanto starters are worth shit, same for some other popular mons like Froakie and Torchic. Even Mawile has been losing steam through the days.
Try fossils, Larvitar, or whatever obscure mon you have. The better the ball the higher you can put the price.