I think there are a lot of proteins out there that are either way overrated or quite underrated.
For example, while I like dorado (or dolphin), I think it's way overrated, especially when people call it mahi-mahi. There are much better fish out there in my opinion, but it has become exceedingly trendy.
I also think "Black Angus" beef is overrated. If an angus and, say, a Hereford were both raised properly and slaughtered at the appropriate time, one would find it practically impossible to tell the two apart once cooked. The feed and care of the cow, as well as the grading, has much more to do with the quality of beef than the breed alone. In other words, a prime Angus steak that is raised in a grain feedlot to fatten it as quickly as possible will most likely have less flavor than a Hereford that is free range and fed with a balanced diet of grasses.
Now to the underrated. Staying with the bovine theme, marrow (of all animals really) is quite underrated. I think it may be because of a gross-out factor for some, or the fact that it's simply not that abundant by nature, but properly prepared marrow is delicious.
I also think that wild game is underrated. I'm not sure why this is, and maybe I'm reading the attitude of some non-foodies the wrong way, but it appears that some people have an adverse opinion of the culinary qualities of rabbits, venison, squirrels, and the like. Regardless, these little critters make some of the best meals I have personally ever had.
What do you consider to be highly overrated and underrated proteins?