Anthony Caine of For Better or for Worse. Once Lynn Johnston decided to bring Liz "back home" and pair her up with her nice-but-dull first love, Johnston made every effort to make the reader love him as much as she obviously did (and pretty much retroactively vilifying his ex-wife, Therese, in the process). This extended to her having Liz's father John, the strip's patriarch, explicitly put down Liz's other boyfriends, and fawn over Anthony to the extent that he seriously appears to want his daughter to marry the guy mostly because he himself has a crush on him (that Liz's stated goal is to marry a guy just like her father only adds to the Freudian fun). The readership, by and large, rejected any and all attempts at this, as signified by his detractor nicknames "Blandthony", "Granthony" (due to the fact that he looks way older than Elizabeth) and "That Fucking Mustache Guy".
Perhaps reacting to her readership, Lynn 'improved' Anthony by removing his ostensible one flaw - his moustache. And of course, it was Therese who made him grow it against his will in the first place. Despite this concession, the backlash eventually got so bad that Johnston published a defense of the character on her website, in which it turned out that Anthony's overt blandness was in fact the reason we should all love him: he had excellent prospects (specifically, as a mid-level accountant at a local used-car dealership) and besides which Liz' parents knew him and trusted him. Why, yes, the author has proudly admitted to being a "Child of The '50s", why do you ask?
FoxTrot potentially has either Jason or Andy as this role. Jason is due to his increased prominence as the strip went on, getting two several month summer storylines that heavily featured just him and his friends without the other family members and much more appearances in the Sunday-only strips even if just to have someone to deliver the punchline to. That and he's the only cast member that could be reliably used to deliver Bill Amend's tech humor. Andy is also considered to a lesser degree as she often gets the last word and rarely is called out for her own vices and failings.
Frank - ostensibly the central character of Liberty Meadows. At first just the foil for the antics of the Funny Animal cast, towards the end of the strip's newspaper run, he became more and more the focus of events, particularly lead female Brandy's wedding. As the strip made it more obvious that Frank and Brandy were meant to be together, there were fewer and fewer answers to the question "Why, exactly?" Especially given that A) Brandy's fiance was everything Frank wasn't (rich, good-looking, smooth, and actually able to tell Brandy how he felt) and B) Brandy had already told him he'd blown his shot with her by being wishy-washy.
Luann: Mr Fogarty, Luann's teacher. Greg Evans dedicated a full 3 weeks of story to him announcing his retirement (from a job he hates and is terrible at). And within the strips were "flashbacks" showing bits from past stories, emphasizing exactly how one-note he is. And every day a note reminded readers to follow a link to see even more of these past stories. It's doubtful anyone except Evans himself cared much about Fogarty leaving, certainly not enough to go skimming through old storylines just to see numerous examples of him being ignored and disrespected by the students. The "shilled by other characters" part comes into play when the students (Tiffany included) throw him a surprise retirement party, even though the idea of them showing him attention or gratitude goes against 25 years of canon.
Peanuts: Spike (Snoopy's brother) and Rerun (Lucy and Linus's younger brother). Both debuted in the 70s but dominated much of the strip's final two decades (Spike the 80s, Rerun the late 90s). Even diehard fans had their patience tested by the repetitive gags involving Spike interacting with a cactus. Rerun seems to have caused a Broken Base. Some fans resented him for upstaging the classic characters, others thought that Charles Schulz managed to pull off a successful Rescue From The Scrappy Heap (prior to the 1990s he was almost exclusively known for strips where he rode on the back of his mother's bicycle, and made terrified comments about her absurdly scary cycling skills).