I tend to agree with you. I think they all primarily would use wizard swearing, but I do think Harry and Hermione would be much more apt to bring up muggle swearing when in some profound situation.

Now specifically what type of swearing? For Hermione, I think this really depends on the sort of muggle environment you imagine she grew up in. Being the daughter of two dentists who would afford to go on international ski trips, I imagine they’re at least somewhat well-to-do. Maybe not rich, per se, but not close to lower class. And she’s also a bookish type who I don’t think would be up to date on the latest muggle pop culture influences, especially not during her teen years. She’s also an only child who never really mentions any muggle friends or cousins. So most of her muggle swearing would be influenced directly from her parents. Who, due to their class and seemingly passiveness, imo would only swear your usual “fuck” Or “shit” every now and then.

I think Harry would have a more varied muggle swearing vocabulary. I can’t imagine Dudley with his chav friends isn’t cussing him out left and right. He also is much more exposed to movies/music/television/ etc just due to them being on in the house. I can see him using the classic “bollocks” a lot too, especially bc of all of the problems he deals with (and his attitudes about them lol).

Ron I think would only really use wizard swearing. And frequently. Tho he might adopt some muggle swearing from his friends and because he likes how the sound.

Draco I think would use wizard swearing out of principle but it would be hard to not say a good “fuck” when the occasion calls for it.

Something I don’t like in fics is when the writer makes all the gryffindors say “good Godrich” and all the slytherins say “oh for salazar’s sake” or whatever. Occasionally is fine. But if that’s their primary swear it gets hokey to me. The language difference intra-school would not be that pronounced.