This is simple:

Overrated: I feel like Bards are a bit overrated - whenever I've actually seen one in play (or played one), the results have been kinda disappointing. I don't deny that they have a high optimization ceiling, but there are a lot of ways to mess them up (as compared to 3e, where "spam Inspire Courage" was always a workable plan).

Underrated: The Monk. Seriously, they're a solid class (which surprises me, given how often D&D screws up the monk thing). They are unfairly denigrated by a paradigm that overly favors damage as the primary optimization metric!

Irrational Hate: I hate Paladins as a class. Oh, it's nothing on paper - it's just that I played a Paladin in one of the most uncomfortable one-shots I've ever been in, and so they are entirely tarnished. Which is a shame, because I like the whole holy warrior thing - I still want to sit down and play my Celestial Bladelock "Paladin" in a game that isn't the DM wanting to be an auteur...