My 2 (3?) cents:
Worst class in terms of performance: Inventor. The Inventor really feels like half a class to me, in large part because I don't think they deliver at all on their fantasy of letting you be creative and invent things on the fly. In my opinion, they could be this fantastic provider of diverse item-based utility, but in practice it feels like they play like a clunkier, less reliable, and generally less effective Barbarian, the absolute last class I would normally want to compare to a brainy inventor type. I don't find the class at all fun to play, and although I can acknowledge that they're not completely useless, it feels like other classes do what they can do better and in more interesting ways.
Worst class in terms of flavor: Oracle. When Player Core 2 was on the horizon, I was really hoping for the Oracle, a flavorful but otherwise really weak class, to receive targeted buffs that would let them feel really powerful for leaning into their curse. What got released instead was a class that was undoubtedly very strong, but that in my opinion took the main thing that made the class unique, and sidelined it almost entirely. You can completely ignore the class's curse mechanic right now, and you'd still be one of the strongest casters around due to your 4 spell slots per rank and beefy base stats, and what's worse, it's often better to play the class exactly like that. What was once one of the most flavorful and interesting spellcaster classes became the most generic, and that makes me a bit sad.
Worst class in terms of mechanical design: Animist. In terms of flavor, the Animist I think is incredible, as they bring this whole new dimension to divine magic and shine as a mortal link to the divine that differs radically from the Cleric. Communing with ancient apparitions and having them as your traveling companions makes for some amazing roleplaying opportunities, and gives additional characters to forge bonds with over the course of the campaign. Except, unfortunately, the class's mechanics don't focus on any of this at all in my opinion. Instead, the Animist to me is the ultimate Main Character Syndrome class, no small feat given that they were released in the same book as playable demigods. The class is designed to step on virtually every niche in the game, lets you tread on multiple niches simultaneously, often lets you tread on a niche better than the actual specialists in those niches, and as the icing on the cake, lets you completely swap which niches you want to step on from one day to the next. The fact that the Animist can swap out not only their spells, but also their apparitions and even their class feats from day to day undermines any roleplaying that could have come from committing to specific apparitions and bonding with them, but also means all Animist builds inevitably converge into the same build, particularly as nearly everyone picks the Liturgist for being so head-and-shoulders above the other subclasses. The class is far too versatile for their own good, and in my opinion is grossly overpowered in a manner that heavily threatens the play experience of their teammates. Were the class more popular and less inaccessible due to their significantly above-average complexity, they would probably be causing far larger balance problems right now.