Might I chime in?
I don't like Hunter x Hunter. Tried giving both adaptations a watch, but they just weren't my cup of tea - and hearing about the constant hiatuses the manga goes through because of its author's health has discouraged me from reading it. The only reason I'm interested in it is to hear Hisoka's 1999 English dub voice - that of Brendan Hunter, who also (exaggeratedly, but exquisitely) voiced Elec Man in Mega Man: Powered Up.
On a related note, since the creators of this and the aforementioned series are spouses, I like the 90s anime adaptation of Sailor Moon better than the manga or Crystal. I just prefer the cuter art style over the uncanny doll-like designs for the characters, not to mention the anime's stories are generally more uplifting.
My last unpopular opinion is that Konjiki no Gash (Bell) isn't unpopular or underrated anymore. It got a sequel, for crying out loud! Honestly, though, it should have stayed down. Some of the jokes in it are extremely outdated, and the premise, while hopeful on the surface, is actually extremely depressing - which the sequel has dialed up to eleven. I used to love it, once upon a time, but now I just want it to fade into obscurity.