To me one of the most underrated fish is common Paradise fish (Macropodus operculatus), they tolerate temps from below 50'F to almost 100'F, will tolerate low oxygen conditions, and are still beautiful. I kept some in my rain barrels spring thru fall in Wisconsin to eat mosquito larvae, and could always count on pulling a few juvies out in fall.
The most "Over Rated" fish to me, are flower horns, BPs and any other designer fish.
My paradise fish was psycho, she ate most of her tank mates (WCMM, Danios) and started chasing panda cories. She was a survivor though, on first night she jumped out of the tank and was dried on floor, don't know for how long, I picked her, she moved, I immediately added her to tank, she survived. Definitely underrated fish.
Flowerhorns and BPs are getting favored due to aggressive personalty which is mistaken for affection. Majority of crowd that gets attracted does seem weird to me. I have seen some cool hobbyist falling for those as well. RD has few, one of members on my FB group is vet, has Marine tanks, breeds see horses keeps one too, but I would say those are minority.