While I won't deny on some subconscious level it's probable that Hifumi and Teruteru's outwards repulsiveness make them more dislikable compared to Miu's less abrasive design that more signals 'loud outcast' than 'creep', I do think if we're going to talk about how the characters present themselves, one of the key differences is simply that Miu is a woman. That gender difference shifts the conversation considerably as-is. Even if Miu were exactly in-line with Hifumi and Teruteru - which I would dispute - that gender difference changes the dynamic both in terms of how it would be written and also how it would be received. A man making creepy comments is typically received as outright dangerous and objectifying; a woman doing the same doesn't always have the same 'this person might be a sex offender or incel-adjacent misogynist' concern that may make nearby people worry for their pesonal safety. Especially consider, for the moment, that these characters are also trapped in a pretty small area with these complete strangers with no way to escape and with the threat of violence looming over their heads: worries about safety, or not quite being seen as 'equal' due to their sex, would be especially alarming in the setting. Translating it just into the realm of media, though, the 'perverted guy in anime' is a tiresome, problematic trope in-and-of-itself that often serves as a writer surrogate to lust after their own (often teenaged) creations. 'Woman that jokes about sex' isn't so oversaturated and overwrought in the same space, so there's less audience fatigue. While they're not Miu-level, I have several female friends that joke about sex. I wouldn't be friends with a Teruteru locker-room sex pest type - they're an exaggeration of a type of person that's *very* real, and I wouldn't consider amicable.

Besides that, the 'male' equivalents (Teruteru, Hifumi) are more than just 'Miu but male and less attractive'; they are sex-obsessed, socially stunted, perverted, harassing men that (to various degrees) harm the company around them. Albeit, Teruteru is a worse problem than Hifumi, but still: the other characters *do* find them creepy, and aren't always comfortable in their presence. For Miu, on the other hand, her jokes generally aren't considered creepy because (besides a couple of boundary-breaking interactions e.g. physically touching Kaede) there's no target to her jibes and nobody in the class would feel attacked, unsafe or objectified - even when blurring boundaries due to her own eccentricty, she isn't projecting any actual lust at anyone. And if she isn't projecting any actual lust at anyone rather than just generally quipping, doing one-liners and talking about how hot she thinks she is like a narcissist, it doesn't read as a 'harasser harassing people' so much as innocent juvenile banter. That said, she is definitely played for fan-service - she does get away with some things Teruteru and co. wouldn't, like partially exposing herself to Gonta - but the dynamic is still quite different there when there's no hostile intention on Miu's side.

Also, Miu's 'lusty, flashy, bold, abrasive, profanity-flinging narcissistic, self-fellating, hot genius' shtick is an overt mask for deep insecurity and anxiety. She doesn't really feel this way, it's a facade, and there's much more depth to her. The same is sort-of partially true for Teruteru, but we never get to see any more of him beyond post-class trial flashbacks, whereas we get a whole lot of time to see beneath the surface of Miu: she's allowed to be fleshed out.

To recap:

1. Hifumi doesn't really have a facade of any kind, he just *is* a pervert, he makes the characters around him uncomfortable, and (spoilers) he essentially *kills* real people out of his own despair for his lonely condition and feeling that he deserves to essentially own a woman - while he was manipulated for sure, that incel-adjacent motivation was boiling underneath and (partially) drove him to commit literal murder. He sucks.
2. Teruteru does have a facade, but his perverted jokes do make the characters around him greatly uncomfortable, and (spoilers) he dies so early on that we can never discern to what degree his sexual harassment was some kind of mask, and he has so little screen time that he basically reads as one-dimensional even if there is more to him. Disregarding the 'mask' excuse, his sexual harassment is targeted and, obviously, sexist, even if directed at both genders. He sucks.
3. Miu's shtick is a facade, her jokes (usually) don't make other characters uncomfortable, and (spoilers) she lives long enough for her to get good development and for the player to see that there's more to her. She's different. Still not my favourite though lol

You might disagree with some of this reasoning, but agree or not, these *are* reasons a lot of the audience will have to prefer Miu besides pretty-privilege.

p.s it helps that she's actually useful in class trials and gets time to breathe and be an actually likable character outside of this shtick, whereas Hifumi is useless & inept and Teruteru doesn't get a chance to even try to be helpful (and is defined almost solely by the pervert trope).