Take this with a grain of salt, as mine lacks significant experience, but:
Overrated: Esoterica offerings. They sound amazing, but also remind me too much of many limited release cigars I chased for too long. I would love to try them ,and will, but in the end have always been able to find something just as satisfying in the realm of regular production.
Underrated: Peter Stokkebye bulks. Price factored in, this is cheaper in many cases than OTC tobaccos, and seems to perform beautifully and consistently. Just like my coffee, I love finding all the varied nuances of differing varietals, nationalities, and roast qualities, but have something clean, rich, and CHEAP, by the several pounds, on hand at any given time. o)