Well Dreamer is definitely in the top of the "meta" overpowered things so might not wanna go that route.
Wong & Ulix are both of the crazy mechanic scale in Bayou, and Zipp is the pirate king of crazy lore. Currently Ophelia is the cheapest entry in the whole game as the entire keyword is in 2 boxes; her mechanics are unique and her lore is good
Lucius is very high risk high reward, unique mechanics & impeccable lore, with a steep.... STEEP learning curve; I wouldn't recommend as a first master because it's so hard. But, I've seen people do it and come out amazing, eventually. Zoraida is also similar to Lucius in a different way, but also in that "meta" overpowered things group.
Keeping in Neverborn, Euripides is the next most unique mechanic but minimal lore because he's new.
The other more unique mechanics that are not dominating the scene are Leveticus in Outcast, Marcus in Arcanists/Neverborn, Jack Daw in Resserectionists/Outcast, Jacob Lynch in Ten Thunders, & Maxine Agassiz in Explorer's Society (but her stuff is not out yet).