Most underrated imo are carbon steel folded sheet metal folders designed from 1869 to 1929. Namely, the Douk-Douk, K55 Mercator, Opinel, Higonokami. To me, these knives are the bee's knees. Fifteen bucks for the base models of 'em, a bit more can get you pocket clips on things like the Mercator. That was invented in 1869, that was the original "Buck 110" for me! I feel like they came around a hundred years later and reinvented the lockback, it's so old it's new at that time.
All of these are superb cutting tools and I own them all, and intend to get their variations, too, like the Tiki Douk-Douk, Brass Otter Mercator, stainless versions, oh man, the Higonokami has the most variations of all of these, from basic carbon Aogami to Shirogami and VG-10, I would love to explore this knife further. As I continue into the worlds of wood and leatherwork, I will find more tasks for them. But boy, these are competent, affordable, and classic slicers. You can often find one of these knives on my person, with a slipjoint and a Spyderco. Mora is fixed-blade, but they could roll with all the above guys, Modele Depose and Otter and Opi.
Over-rated? I don't know... maybe one of those huge fat folders like a Strider? I have never fairly handled one, though, so I won't say for sure. I just know if I'm going to carry a big knife, it will probably be something with a Demko lock. I have so far thoroughly enjoyed all my knife purchases ever since my last BudK purchase in 2019 made me buy my first Ontario SP-1, Mora Precision and Opinel no. 8. Those were my introductions to the world of good knives! From that ill-fated BudK purchase, I have a terrible Paki F/S dagger, three neck tantos and two liner-lock daggers, one of which was the only lock to fail on me, and it did so while just opening, slipped to the show side. But I don't know if you could call them "over-rated". They are rated very low. I do have a sick 6" stiletto of classic looks, so that one is cool.